I need help with a Mouse Tracking challenge

Hi.  Im trying to do the challenge where numbers follow my mouse.  Which I can do, I can get the numbers to follow the mouse, but, they also want the numbers to increase or decrease as moving the mouse.

I can not figure out how to make the numbers grow. (not in text size) but grow numerically up or down.

I don't know how to write the variable to do this.    thanks in advance.