Tax Rates. Based on the amounts of taxable income below, compute the federal income tax payable in 2019 on each amount assuming the taxpayers are married filing a joint return. Also, for each amount of taxable income, compute the average tax rate and the marginal tax rate.

a. Taxable income of $30,000.

b. Taxable income of $100,000.

c. Taxable income of $375,000.

d. Taxable income of $700,000.