Jack and Joe leave their homes at the same time and drive toward each other. Jack drives at 60 mph, while Joe drives at 30 mph. They pass each other in 10 minutes. How far apart were Jack and Joe when they started?

The bottom half of Lincoln's paper was blanketed with an indecipherable mess of scribblings, half-finished equations and eraser shavings. Normally, math came easy to him, but this problem was frustrating the bejeezus out of him. No matter how many times he scoured his class notes, it seemed like nothing he had learned thus far was relevant.

"So do I add their two speeds together, or divide it by the time, or… GAH!"

It didn't help that a particularly noisy thunderstorm was bellowing outside his door. Every time he thought he was on to something, a flash of light or a clap of thunder would interrupt his train of thought.

He collapsed onto his desk and heaved out a defeated sigh. There was no way he would solve it at this rate: not by himself, at least. It was time to call in the family tutor… Lisa.

He stepped out of his room, walked up to Lisa and Lily's, and carefully crept open the door, out of fear that he might be interrupting one of Lisa's highly volatile experiments. That, or Lily's sleep cycle.

Fortunately, he wasn't interrupting either. Lily was playing in her crib, happily cooing to herself. His parents had given her a fluffy pair of earmuffs, so she wouldn't be spooked by the storm. Lisa, meanwhile, was nowhere to be seen.

Dang it.

Lincoln proceeded to knock on all of the other doors on the top floor, asking each of his sisters if they had seen Lisa. He got little more than a shrug from the twins, Lucy and Lynn, and he knew better than to disturb Lori in the midst of one of her text-a-thons with Bobby.

He knocked on Luna and Luan's door, and was promptly greeted with a raspy, "Come in, dude!" from inside. He walked in to see Luna tuning her guitar and Luan sorting her box of props.

"Have either of you seen Lisa?" asked Lincoln.

"Can't say that I have," said Luan. "Have you tried asking her roommate?"

"Well, I haven't, but-"

Then it dawned on him.

"Very funny, Luan," he grumbled, while Luan collapsed into a giggling fit.

"I saw her running down the stairs 'bout thirty minutes ago, when the storm started up," said Luna. "Dunno how much that helps you, but it's something."

Well, at least now I know where to look, thought Lincoln. "Thanks, Luna!"

"Any time, bro!"

With that, Lincoln bounded downstairs. "Lisa?" he called, scanning the living room for any possible sign of her. "You in here?"

Before long, he was greeted with the sight of two tiny feet peeking out from under the couch. Curious, he walked over, crouched down and tapped one of the feet. "Is that you, Lisa?"

Lisa squeezed her head out from under the couch with a pop and looked up to greet her big brother. Her hair was more than a little frazzled, and she had an incessant twitch in her eye. "Oh, um, hello, Lincoln! Fancy seeing you here!"

Lincoln gave her a peculiar look. "Any reason why you've decided to hide under the couch?"

"Hiding? No, Lincoln, I'm… I'm conducting a study on sofa lint. Very complicated. You wouldn't understand."

Lincoln rolled his eyes. "Well, see, I need some help with this math problem. Mind coming up and taking a look at it?"

"NO!" exclaimed Lisa. "I mean- not right now. I must finish my study. I'll be out in…an hour. Or three."

Lincoln eyed Lisa skeptically. Something wasn't right here.

"Lisa, are... are you afraid of the storm?"

"What?! Of course not!" cried Lisa, punctuating her sentence with a nervous chuckle. "Why would I be? How ridiculous."

"Lisa, it's okay. If you're afraid, you can tell me."

Lisa stood up, brushed herself off and looked Lincoln straight in the eye. "Lincoln," she began, taking on her default tone of condescension, "thunder is nothing more than a harmless by-product of the rapid expansion of air caused by lightning. There is no rational reason to be afraid of-"

*BOOM*

"Eep!"

Lisa ducked back under the couch, trembling all the while.

It was rare for Lincoln to see the young prodigy so blatantly proven wrong, and normally he'd take the opportunity to engage in a bit of gloating and teasing. But it was just as rare for him to see her so childlike and vulnerable, and his heart melted at the sight of his sister's cowering form.

"You want me to hold you until the storm passes?" he asked.

"Y-yes, please," Lisa squeaked, her facade completely destroyed.

"All right, get up here," said Lincoln, smiling warmly at his little sister. He bent down, picked her up and plopped himself down on the couch, with her in his lap. Immediately, she wrapped her arms around her big brother and buried her face in his chest, quivering.

"It's okay," he whispered, stroking her hair. "Everything's gonna be okay. Lincoln's got you. Shh…"

Lisa grew calmer with every successive stroke, and before long, her quivering petered out. After a few more minutes of cuddling, she shut her eyes, popped her thumb in her mouth and started sucking on it contentedly.

She's more of a toddler than she lets on, Lincoln thought.

Lincoln left Lisa curled up in his lap until the rain let up and the sound of thunder slowly faded away- and a little bit after that, in fact. He got so comfortable with his baby sister that he almost forgot why he was looking for her in the first place.

Almost.

"Lisa?" Lincoln said, nudging her awake. "The storm's over, Lisa. You can get up now."

"Mmm?"

It took a couple of seconds for the gears in Lisa's prodigious brain to start turning again. As soon as she realized where she was, she hastily withdrew her thumb and dismounted from the couch.

"Thank you, Lincoln," she said. "Your emotional support was greatly appreciated."

"Glad to hear it. Now, about that math problem…"

"Oh! Of course."

Lisa trotted up the stairs and over to the far side of the hall, with Lincoln by her side. Once they got to his door, Lincoln unlocked it, pushed it open and gestured for Lisa to let herself inside.

"It's on my desk," he said. "I-I don't even know where to start!"

Lisa walked in, hopped onto Lincoln's chair and took a look at the problem, rubbing her chin as she perused it a few times over. Figuring out the answer wasn't the hard part; she had done that easily. The challenge was explaining it to Lincoln in a way he would understand.

"It's quite simple," she said. "You just need to calculate how far each car can travel in ten minutes. Then you add the distances together."

Lincoln gasped. Of course!

He grabbed a pencil off his desk and started scribbling out equations. "Let's see… Jack is going 60 miles an hour, which means he's going one mile every minute… and Joe is going half a mile per minute… so in ten minutes, Jack goes ten miles and Joe goes five… so the answer is…

"Fifteen miles?" he asked.

"Correct."

"Thanks, Lisa!" he exclaimed, triumphantly writing "15" in bold at the bottom of the page. "I can't believe the answer was right in front of me this whole time. Boy, do I feel stupid."

Lisa's eyes sunk towards the floor. "No, Lincoln," she said. "I'm the one who should feel stupid."

Lincoln gave her an incredulous look. "For what?! You just solved that problem like it was no big deal!"

"I'm not talking about that," she said with a sigh.

"Then what are you… oh." The shock in Lincoln's eyes melted away. "This is about the storm, isn't it?"

Lisa nodded.

Lincoln picked her up, put her down on his bed, and took a seat next to her.

"Lisa, honestly, it's okay," Lincoln said, draping his arm around her. "Lots of kids your age are scared of thunder."

"That's not the point!" Lisa cried. "The point is that I know I shouldn't be afraid of it. I know it's just a harmless sonic shock wave, but it…"

She looked up into Lincoln's eyes; tears were welling behind her glasses. "It still scares me, Lincoln. It really does."

"Aw, Lisa…"

Lincoln pulled her in closer, took off her glasses and started dabbing away her tears. "Fears don't always make sense. Sometimes you can't explain why you're afraid of something; you just are.

"It's a feeling deep in your gut, Lis'," he added, patting his stomach for emphasis. "And your gut doesn't always listen to your brain."

Lisa looked down at her own stomach. "I guess it doesn't."

"Nope!" said Lincoln. "In fact, lemme give you an example. Don't tell Lori I told you this, or she'll turn me into a human pretzel, but, um…"

He donned a mischievous smirk. "She's afraid of puppets."

Lisa snickered. "Really?"

"Yeah, no joke. It took her months before she got comfortable around Mr. Coconuts. One time Luan just left him on her face while she was sleeping. You should've heard her scream when she woke up."

The two of them shared a good, hearty laugh.

"Point is..." Lincoln said, regaining his composure. "Point is, there's no reason for her to be scared. She must know that Mr. Coconuts is just wood and felt, right?"

"As Lori is of average intelligence, I would assume so," Lisa responded.

"But she still gets scared around him. No reason, she just does. Are you getting it now?"

Lisa let out a relieved sigh. "Yes. I believe I am."

"There's nothing shameful about getting scared when it's stormy outside. And there's definitely nothing shameful about running to me when it happens."

Lisa wiped her eyes dry, put her glasses back on, and gave her brother a brave smile. "Thank you."

She leaned in and reached her arms out towards Lincoln, who responded by snatching her up and putting her in a bear hug.

"Of course," he said. "What are big brothers for?"