A division of Ditton Industries manufactures the Futura model microwave oven. The daily cost (in dollars) of producing these microwave ovens given by the following function, where x stands for the number of units produced. C(x) = 0.0002x³ -0.06x² + 120x + 5000 (a) What is the actual cost incurred in manufacturing the 121st oven? The 231st oven? The 311st oven? (b) What is the marginal cost when x = 120, 230, and 310?