13. Assume that in year 1 you pay an average tax rate of 15 percent on a taxable income of $25,000. In year 2, you pay an average tax rate of 20 percent on a taxable income of $50,000. Assuming no change in tax rates, the marginal tax rate on your additional $25,000 of income is Select one: a. 13 percent. b. 35 percent. c. 30 percent. d. 25 percent