There are 2 problems I don't understand, and would appreciate if someone could explain how to do them:

Find lim h→0 for [f(3+h)-f(3)] / h if f(x) = x^3

Use the limit definition to find the derivative at the indicated point: f(x) = -x^3 + 4x^2, at (-1,5)

The first one is simply the definition of the derivative, at x = 3. Differentiate x^3 and plug in 3.
f '(x) = 3x^2, f '(3) = 3(3)^2 = 27

The second one you have to find the derivative using the limit definition, so evaluate the limit as h->0 of (((-x + h)^3 + 4(x + h)^2) - (-x^3 + 4x^2)) / h), then plug in -1. You should get f '(-1) = -3(-1)^2 + 8(-1) = -3 - 8 = -11.