Scot and Vidia, married taxpayers, earn $42,000 in taxable income and $5,000 in interest from an investment in City of Tampa bonds. (Use the U.S. tax rate schedule for married filing jointly). (Do not round intermediate calculations. Round your answer to 2 decimal places.) a. If Scot and Vidia earn an additional $21,250 of taxable income, what is their marginal tax rate on this income? b. How would your answer differ if they, instead, had $21,250 of additional deductions?