Consider the Following Table for a Firm

Multiple Choice

Consider the following table for a firm.The first column shows the number of units of a variable factor of production employed by the firm.
TABLE 13-2
-Refer to Table 13-2.Suppose the firm is a perfect competitor and faces a given price of the product equal to $2 per unit.The marginal revenue product of the 5th unit of the factor is

A) $128.
B) $148.
C) $20.
D) $40.
E) $2.