The cost (in dollars) of producing a units of a certain commodity is C(x) = 5500 + 15x + 0.4x2 (a) Find the average rate of change of C with respect to a when the production level is changed (i) from x = 100 to x = 105. Average rate of change = (ii) from r = 100 to x = 101. Average rate of change = (b) Find the instantaneous rate of change of C with respect to x when x - 100. (This is called the marginal cost.) Instantaneous rate of change =