suppose a certain business pays 10% tax on its first $10,000 income, 12% tax on income above $10,000 but below $40,000, and 22% tax on income above $40,000. Suppose the business earns $50,000 in income this year. Its marginal tax rate is __________.

a. greater than 22%

b. 10%

c. 12%

d. 22%