Harriet and Harry Combs $($both $37$ years old$)$ are married, and both want to contribute to a Roth IRA. In the $2024,$ their AGI before any IRA contribution deductions 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?