Hello I'm having a hard time answering problem 15

(a) (4f - 13g) (3) (b) (fg)'(3) (c) (3) (d) (f- 3 (15) If f(x) = 3 cos x - 8 sin z, find f'(x) and f"(x). (16) In each case, find the derivative of the given function in simplest form. (a) a(r) = 75p-r2 ( b ) k (t ) = 1 + sin 5t ( C) H()