What is the AGI limit above which each of the following taxpayers would not be eligible to receive a credit for the elderly or the disabled?

not

a.A single taxpayer eligible for the credit who receives $1,900 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.

c.Taxpayers filing a joint return, and both are eligible for the credit and received $3,900 of nontaxable Social Security benefits.