Please help with explanation!

For each of the given functions f(@), find the derivative (f-1) (c) at the given point c, first finding a = f (c). (See Theorem 7, page 156 of the Stewart Essential Calculus textbook) 1. f(x) = 4x + 7x2; c=-11 ( = (f-1)' ( c ) = 2. f(a) = x2 - 15x + 71 on the interval [7.5, co); c = 17 0 = (f-1)' (c) =]