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 $3\mathrm{.}5.$ Assume that their taxable income this year was $$197,000.$ 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.