The table displays data for a small, competitive, profit-maximizing firm that produces and sells envelopes. Labor (Number of workers) Marginal Product of Labor (Boxes of envelopes per week) Wage (Dollars per worker per week) 0 1 134 600 2 106 600 3 92 600 4 84 600 5 78 600 Refer to Table 19-7 . Suppose the firm sells each box of envelopes that it produces for $6. What is the marginal profit of the fourth worker? a. $132 b. $132 c. $504 d. $96