(Table: the Market for Power Tools, Marginal Revenue Product of Labor

(Table: The Market for Power Tools, Marginal Revenue Product of Labor and Demand) Use Table: The Market for Power Tools, Marginal Revenue Product of Labor and Demand. In the table, the total product of labor is shown for the hourly production of power tools. Assume that the market for power tools is perfectly competitive. If the price of a power tool is $2, and the wage rate is $90 per hour, the profit-maximizing quantity of labor is _____ workers. $${ \begin{array} { l } \text { Table: The Market for Power Tools, } \\\text { Marginal Revenue Product of Labor and } \\\text { Demand }\\\end{array} } \\\begin{array} { | l | l | } \hline \text { Quantity of Labor } & \text { Total Product } \\\hline 0 & 0 \\\hline 1 & 20 \\\hline 2 & 50 \\\hline 3 & 90 \\\hline 4 & 120 \\\hline 5 & 140 \\\hline 6 & 150 \\\hline 7 & 150 \\\hline 8 & 140 \\\hline\end{array}$$

A) zero
B) two
C) four
D) six