Campbell, a single taxpayer, earns $428,000 in taxable income and $2,560 in interest from an investment in State of New York bonds. (Use the U.S. tax rate schedule). Required: a. If Campbell earns an additional $16,400 of taxable income, what is her marginal tax rate on this income? b. What is her marginal rate if, instead, she had $16,400 of additional deductions? (For all requirements, do not round intermediate calculations.) a. Marginal tax rate b. Marginal tax rate % %