The Figure Below Shows the Cost and Revenue Curves for a Monopolist

Multiple Choice

The figure below shows the cost and revenue curves for a monopolist. Assume that the marginal cost of production is equal to the average total cost at the profit maximizing output level. The maximum profit for this monopolist if he does not practice price discrimination is _____.​ ​
Figure 9.4
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A) $4
B) $14
C) $3.50
D) $21
E) $4.