A monopolist faces a demand curve given by $P=60-2Q$ and has total costs given by $TC=Q^2$. Now suppose that the country in which this monopolist is located decides to engage in international trade. The world price of the product produced by the monopolist is $10. What is the firm's profit-maximizing output level?
$P=10\implies 10=60-2Q\implies 2Q=50\implies Q=25$
Unfortunately, this isn't the right answer. How do I solve this problem?