Susan and Stan Britton are a married couple who fle 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 $279,000. Dog not round intermediate calculation. a. What is their federal tax liability? Round your answer to the nearest doilar. 5 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