The Following Table Shows Output Per Hour Produced by the Different

The following table shows output per hour produced by the different units of labor. Table 28.1
The marginal revenue product of a resource is equal to the product of the marginal product of an input and marginal revenue.
According to Table 28.1, if the wage rate is $9 per hour, how many workers should this firm hire?

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