A firm's manager is given the following information: To sell 4 units of output, a price of $132 must be charged; this level of output reflects marginal revenue of $102 and marginal costs of $60. If the firm wants to sell 5 units of output, a price of $122 must be charged; this reflects marginal revenue of $82 and marginal costs of $70. To sell 6 units of output, a price of $112 must be charged; at this level of output, marginal revenue will be $62 and marginal costs $80. What should the manager do?

A. Produce 6 units of output and charge $112.
B. Produce an amount less than 4 units.
C. Produce an amount greater than 6 units.
D. Produce 4 units of output and charge $132.
E. Produce 5 units of output and charge $122.