The cost (in dollars) of producing x units of a certain commodity is given below. C(x) = 3000 + 15x + 0.15x^2

(a) Find the average rate of change of C with respect to x when the production is changed from x = 100 to the given value.
(i) x = 102

(ii) x = 101

(b) Find the instantaneous rate of change of C with respect to x when x = 100. (This is called the marginal cost.)
$ /per unit