A firm is a competitive seller of output at amarket price of $3. The only resource itrequires to create its product is labor, which itpurchases competitively at a wage rate of $6per hour. The last worker it employs increasestotal output from 36 to 40 units per hour.What is the marginal revenue product for thisworker?(A) $3
(B) $6
(C) $12(D) $24
(E) $40