Harriet and Harry Combs (both 37 years old) are married and both want to contribute to a

Question:

Harriet and Harry Combs (both 37 years old) are married and both want to contribute to a Roth IRA. In 2015, their AGI is $50,000. Harriet earned $46,000 and Harry earned $4,000.
a) How much can Harriet contribute to her Roth IRA if they file a joint return?
b) How much can Harriet contribute if she files a separate return?
c) How much can Harry contribute to his Roth IRA if they file separately?