I am studying for the Calculus Clep exam and I am having trouble understanding how to find the derivative of the inverse of a function.

Here is the problem I am having trouble with and what I have done with it:

-------------

Let . If is the inverse function of , then (A) (B) (C) (D) (E)

I believe . If so, then and but this is not the answer. Am I mistaking an for a or something like that? Also, if that is not the correct general equation to find the derivative of the inverse of a function, what is it?

Thank you!

Raul