From part (a) you know the equilibrium market price is $400. You also know that
the firm profit maximizes by producing that level of output where MR = MC.
Since the equilibrium market price is the firm’s marginal revenue you know that
MR = $400. Setting MR = MC gives you 400 = 2q + 1, or q = 199.5. Thus, the
profit maximizing level of output for the firm is 199.5 units when the price is
$400 per unit. Using this information it is easy to find total revenue as the price
times the quantity: TR = ($400 per unit)(199.5 units) = $79,800. Total cost is
found by substituting q = 199.5 into the TC equation: TC = $40,099.75. Profit is
the difference between TR and TC: Profit = TR – TC = 79,800 – 40,099.75 =
$39,700.25. Since profit is not equal to zero this cannot be a long-run equilibrium
situation: it must be a short-run equilibrium situation.