In a small town, there's a mousepad factory which employs workers at $10 an hour, for forty-hour weeks. There is an old composer in town, who expects to complete an opera in about 9 months time. On the other hand, if he were not composing, he would give harp lessons, and charge his students $12 an hour. What is his opportunity cost in writing his opera? Explain the assumptions you made in deriving this answer