(9 points) The average cost (in dollars per item) to produce a items is given by C(x) = 0.04x2 - 1.2x + 13, for z > 0. (a) What is the total cost, C(a), of producing a goods? C(a) = dollars. (b) Find the marginal cost function, C' (x). C'(x) = (c) Notice that C'(x) is a quadratic function. Find the vertex. Using the vertex, we see that the minimum possible value of the marginal cost is dollars per item. (d) Find critical values and any max or min points of C(a) . Use to complete the following sentence: The average cost is at a minimum when goods are produced at an average cost of $ per item. (e) Compute the marginal cost at x = 15. C' (15) =