A monopolistically competitive firm is currently producing 20 units of output. At this level of output the firm is charging a price equal to $20, has marginal revenue equal to $12, has marginal cost equal to $12, and has average total cost equal to $24. From this information, we can infer that

a. the firm is earning zero profit

b. the profits of the firm is negative

c. the firm is currently maximizing its profit

d. firms are likely to leave this market in the long-run

Why is the answer c?