Rex and Dena are married and have two children, Michelle (age 7) and Nancy (age 5). During 2012, Rex earned a salary of $24,000, received interest income of $300, and filed a joint income tax return. Dena had $0 gross income. Their earned income credit for the year is: a.) $0 b.) $421 c.) $4,815 D.) $5,236 e.) none of the above