A demand function is p = 400 − 2q, where q is the quantity of the good sold for price $p.

(a) Find an expression for the total revenue, R, in terms of q.
(b) Differentiate R with respect to q to find the marginal revenue, MR, in terms of q. Calculate the marginal revenue when q = 10.
(c) Calculate the change in total revenue when production increases from q = 10 to q = 11 units. Confirm that a one-unit increase in q gives a reasonable approximation to the exact value of MR obtained in part (b).