Here's a hint:

There is no math involved and a 4 year old would get it in a second! 

Now, think about it again... (Boy! I mess up my college kids with this one all the time!)

When you've given up, you can scroll down - the solution is at the bottom of the page.

Solution:

The "straight" letters are above the line and the "curvy" letters are below!

Now, go drive your friends nuts with this one!