In 2020, Joan is claimed as a dependent on her parents' tax return. Her parents report taxable income of $500,000 (married filing jointly). Joan did not provide more than half her own support.

What is Joan's tax liability for the year in each of the following alternative circumstances? Use Tax Rate Schedule, Dividends and Capital Gains Tax Rates, for reference. (Leave no answer blank. Enter zero if applicable.)

a. She received $6,300 from a part-time job. This was her only source of income. She is 16 years old at year-end.

b. She received $6,300 of interest income from corporate bonds she received several years ago. This is her only source of income. She is 16 years old at year-end.

c. She received $6,300 of interest income from corporate bonds she received several years ago. This is her only source of income. She is 20 years old at year-end and is a full-time student.