Answer: The correct answer is c. decrease the amount of labor supplied at any real wage.
Explanation:
When the average tax rate increases while the marginal tax rate is held constant, it means that a higher proportion of a person's income is being taxed. This reduces the incentive to work because individuals are effectively taking home a smaller share of their earnings. As a result, people may choose to work fewer hours or decide not to work at all, leading to a decrease in the amount of labor supplied at any given real wage.