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 hires each unit of labor for $600 per week, and each unit of output sells for $9. What is the value of the marginal product of the third worker? a. $675 b. $600 c. $810 d. $540