Cost of Producing Surfboards The total cost C(x) (in dollars) incurred by Aloha Company in manufacturing x surfboards a day is given by the following function. C(x) = −8x2 + 500x + 120 where (0 ≤ x ≤ 15) (a) Find C '(x). C '(x) = (b) What is the rate of change of the total cost (in dollars) when the level of production is 12 surfboards a day? $ per surfboard