Chuck, a single taxpayer, earns $57,500 in taxable income and $19,500 in interest from an investment in City of Heflin bonds. (Use the U.S. tax rate schedule.) (Do not round intermediate calculations. Round your answers to 2 decimal places.)

a. If Chuck earns an additional $39,500 of taxable income, what is his marginal tax rate on this income?

b. What is his marginal rate if, instead, he had $39,500 of additional deductions?