In 2021, Carson is claimed as a dependent on his parents' tax return. His parents report taxable income of $200,000 (married filing jointly). Carson's parents provided most of his support. What is Carson's tax liability for the year in each of the following alternative circumstances?

a. Carson is 17 years old at year-end and earned $14,000 from his summer job and part-time job after school. This was his only source of income.

b. Carson is 23 years old at year-end. He is a full-time student and earned $14,000 from his summer internship and part-time job. He also received $5,000 of qualified dividend income.