Use the Table Below to Answer the Following Questions

Use the table below to answer the following questions.
Table 12.2.1

-Refer to Table 12.2.1, which gives the total revenue schedule and total cost schedule of a perfectly competitive firm. The marginal revenue received from the sale of the 4th unit of output is

A) $3.
B) $15.
C) $10.
D) $120.
E) $30.