If You Would Have to Pay $5,000 in Taxes on $50,000

If you would have to pay $5,000 in taxes on $50,000 taxable income and $8,000 in taxes on $60,000 taxable income, then the marginal tax rate on the additional $10,000 of income is

A) 30 percent, and the average tax rate is about 13 percent at the $60,000 income level.
B) 15 percent, and the average tax rate is 30 percent at the $60,000 income level.
C) 30 percent, and the average tax rate is 20 percent at the $50,000 income level.
D) 30 percent, but average tax rates cannot be determined from the information given.