The limits below represent f'(c) for a function f and a number c. Find f and c.

a. lim h->0 √(9+h) -3/ h
b. lim △x-> [2+(-3+△x)^3]- (-25)/ △x
c. lim △x->0 ((x+△x)^3 -5(x+△x)^2 +4(x+△x) -7 -(x^3 -5x^2 +4x -7))/△x

a. f(x) = √(x^2 + 6)
b. c = -2
c. f(x) = x^3 - 3x^2 + 2x - 2