She calls me just as I close my eyes. I thought she wanted to say goodnight...

"How can I just leave you like that?... "

"Huhhh?.." I groaned in half sleep.

"Okay now tell me... If F of x comma y is 3axy then what will be fx of it?.."

-.-

I explained it to her for about five minutes. She said thank you as she cut the call. The 'thank you' made my day.

Two minutes later.. she calls. I pick up. "Sorry sorry sorry sorry.. " I thought she wanted to say good night.

"What's Fyy if... "
And that took another five minutes of my sleep.
But every second of those five minutes was worth helping my sister with her math problems. Every second I heard her voice... It made me feel lighter.

Thank you idiot. For being born in my family.