The cost (in dollars) of producing x units of a certain commodity is C(x) = 4,000 + 10x + 0.1x2. (a) Find the average rate of change (in $ per unit) of C with respect to x when the production level is changed from x = 100 to the given value. (Round your answers to the nearest cent.) (i) x = 104 $ per unit (ii) x = 101 $ per unit (b) Find the instantaneous rate of change (in $ per unit) of C with respect to x when x = 100. (This is called the marginal cost. Its significance will be explained in a future chapter.) $ per unit