In a competitive industry the market-determined price is $12. A firm is currently producing 50 units of output, average total cost is $10, marginal cost is $15, and average variable cost is $7. In order to maximize profit, the firm should
a. produce more because the firm is earning a profit of $100
b. keep output the same because the firm is earning a profit of $100
c. produce more because the next unit of output increases profit by $2
d. produce less because the last unit of output decreased profit by $3