A competitive firm sells its output for $60 per unit. Assume that labor is the only input that varies for the firm. The marginal product of the 10th worker is 20 units of output per day; the marginal product of the 11th worker is 16 units of output per day. The firm pays its workers a wage of $150 per day. For the 11th worker, the value of the marginal product of labor is a. $960. b. $1,200. c. $2,400. d. $480.