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