Okay
(So very late, but this may help anyone else who's interested)
Cause it's volume you have to integrate it first to get the y^2 part
Using the form
V = π b∫a y^2 dx
(imagine the b is on the top and a is on the bottom)
You need to make the y=2^x into y^2 = 2^2x
And from there, do your...