Campbell, a single taxpayer, earns $393,000 in taxable income and $12,000 in interest from an investment in State of New York bonds. (Use the U.S. tax rate schedule.) (Do not round intermediate calculations. Round "Federal tax" to 2 decimal places.)

a. If Campbell earns an additional $27,500 of taxable income, what is her marginal tax rate on this income?

b. What is her marginal rate if instead she had $27,500 of additional deduction?