Figure 19-1 A graph of Q versus L shows a curved line, increasing from left to right from the origin and through the following points. (1, 120), (2, 210), (3, 285), (4, 345), (5, 390), and (6, 420). Refer to Figure 19-1. Suppose the firm sells its output for $10 per unit, and it pays each of its workers $400 per week. When the number of workers increases from 4 to 5, the a. value of the marginal product of labor is $450, and the marginal cost per unit of output is about $8.89. b. value of the marginal product of labor is $3,900, and the marginal cost per unit of output is $400. c. firm's profit increases. d. marginal revenue is $450 per unit of output, and the marginal cost is $400 per unit of output