4. /4 points/ Suppose the daily cost function for fridges produced at Friga's Frigid Fridges is represented by the following T.2 C(x) = + 50r + 20, 000 2, 000 50 (a) Find the differential of the daily cost and use it to approximate the cost change if the current production is at 500 units and 5 more units are produced. (b) Find the actual cost difference function and use that to calculate the cost for the 501st unit. (c) Find the marginal cost function, evaluate C"(500), and interpret your results