Marginal Principle: How Many Hours at the Barber Shop? The opportunity cost of your time spent cutting hair at your barber shop is $20 per hour. Electricity costs $6 per hour, and your weekly rent is $250. You normally stay open nine hours per day.

a) What is the marginal cost of staying open for one more hour?

b) If you expect to give two haircuts in the 10th hour and you charge $15 per haircut, is it sensible to stay open for the extra hour? Why?