Please help me with this question? I filled out things but please disregard it.

The cost, in dollars, of producing x units of a particular product is C(x) =12,000+31x +0.08x?. a. Find the average rate of change of C over the interval [60,80] and interpret your result. ((b )- c (a) AROC = Interpretation of AROC= b. Find the instantaneous rate of change of C (marginal cost) when x = 75 and interpret your result. ( ( 75 ) = 37 + C'(75 ) = 314. 16 Interpretation of C'(75) = Let C(x) represent the total cost, in dollars, of producing x items. What are the units of C'(x) ? b. What does the statement C'(100) = 20 mean