The concentration, C in ng/ml of nicotine in the body t minutes after starting to smoke a cigarette can be approximated by C = f(t) = 4te^-0.08t (a) Find f'(t) NOTE: Enter the exact answer. f'(t)= (b) Find f(15) and f'(15) and give units. NOTE: Round your answers to three decimal places. f(15) = ____ ng/minute f'(15) = ____ ng/minute v