The Following Table Shows Total Output Produced by Different Units

The following table shows total output produced by different units of capital. Table 14.3
The marginal revenue product of a resource is the product of the marginal product of the resource and the marginal revenue.
In Table 14.3, if there exists perfect competition in the capital market and the price per unit of capital is ten times the price of the product, the marginal factor cost at the profit maximizing level of employment is:

A) $60.
B) $50.
C) $40
D) $30
E) $20