Robin Owns a Horse Stable and Riding Academy and Gives

Robin owns a horse stable and riding academy and gives riding lessons for children at "pony camp." His business operates in a competitive industry. Robin gives riding lessons to 20 children per month. His monthly total revenue is $4,000. The marginal cost of pony camp is $250 per child. In order to maximize profits, Robin should

A) give riding lessons to more than 20 children per month.
B) give riding lessons to fewer than 20 children per month.
C) continue to give riding lessons to 20 children per month.
D) We do not have enough information to answer the question.