Suppose r(x) =28vx represents revenue and c(x) = 7x represents cost, with x measured in thousands of units. Is there a production level that maximizes profit? If so, what is it? Select the correct choice below and, if necessary, fill in the answer box to complete your choice. O A. Yes, profit is maximized when the production level is units (Simplify your answer) O B. There is no production level that maximizes profit