Consider the following production and cost schedule for a firm. The first column shows the number of units of a variable factor of production employed by the firm.

TABLE 13-5
Refer to Table 13-5. If this firm is perfectly competitive, marginal revenue product (MRP) of the 14th unit of the factor of production is
◦ $20.
◦ $40.
◦ $120.
◦ $1280.
◦ $1540.