help me with this, i am confused

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? AGI Upper Limit a A single taxpayer eligible for the credit who receives $1,700 of nontaxable social security benefits. b. Taxpayers filling 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 $3,700 of nontaxable social security benefits