The Following Table Shows the Marginal Revenue of a Firm

The following table shows the marginal revenue of a firm and the marginal physical product of different units of labor in a perfectly competitive labor market. Table 28.5
Note: Marginal revenue product of a resource is the product of MPP and MR.
In Table 28.5, if the wage rate is $10, how many workers will be employed by a profit-maximizing firm ?

A) 1
B) 2
C) 3
D) 4
E) 5