Hi. I need help with a Maths number.

∫ f(x) dx = (b^2) (e^b) - e

where the upper limit of the integral is b and the lower limit is 1. Also, b > 0

Find an expression for f(x) for all x>0.

I know I have to differentiate the b(sqaure) * e(to the power of b) - e, but I don't really know how to do it since there are no x in the expression. I know I should be using the limits of the integrals as well but I don't know how :/

Help! Thanks x