Assume a company pays tax at a rate of 15% on its first $50,000 of income. Any income above $50,000 is taxed at 25%. If a company has $75,000 of taxable income, which of the following statements is correct?

a. Its marginal tax rate is 15%.
b. Its average tax rate is 25%.
c. Its marginal tax rate is 18.33%.
d. Its average tax rate is 18.33%.