Assuming that an AGI limitation does not apply, what amounts of credit for the elderly or the disabled would be permitted in each of the following instances?

Allowable Credita. A single taxpayer eligible for the credit who receives $$1,400$ of nontaxable social security benefits.b$.$ Taxpayers filing a joint return for which one taxpayer is eligible for the credit and the taxpayers have received no social security benefits.$$0$c$.$ Taxpayers filing a joint return, and both are eligible for the credit and received $$3,400$ of nontaxable social security benefits.