Susan and Stan Britton are a married couple who file a joint income tax return, where the tax rates are based on the tax table 3.5. Assume that their taxable income this year was $331,000. Do not round intermediate calculation. a. What is their federal tax liability? Round your answer to the nearest dollar. b. What is their marginal tax rate? Round your answer to the nearest whole number. % c. What is their average tax rate? Round your answer to two decimal places. %