Directions: You must show work. Partial or full credit will only be given if answers are supported by work. Also, if you have the correct answer but incorrect work to support the answer you will not receive full credit. 1. A company's total sales (in millions of dollars) t months from now are given by S(t) = 3 + Vt (5 pts) a. Find the instantaneous rate of change of sales with respect to time. b. Find S'(25) with the correct units and then write an interpretation of the result. 2. A company manufactures fuel tanks for cars. The total weekly cost, C(x) (in dollars) of producing x tanks is given by C(x) = 20000 + 100x - 0.04x2. (6 pts) a. Find the exact cost of producing the 61st fuel tank. b. Find the marginal cost at a production level of 60 tanks per week and compare your answer to your result in part a