A monopoly firm maximizes its profit by producing Q=500 units of output. At that level of output its marginal revenue is $30, its price is $60 and...

A monopoly firm maximizes its profit by producing Q=500 units of output. At that level of output its marginal revenue is $30, its price is $60 and its average total cost is $34. What is the monopoly's profit?

A. $13,000

B. $15,000

C. $17,000

D. $30,000

I know the correct answer is A, but I don't know how you get that.