Determine the retirement savings contributions credit in each of the following cases:

1. A married couple filing jointly with modified AGI of $37,500 and an IRA contribution of $1,600.

2. A married couple filing jointly with modified AGI of $58,000 and an IRA contribution of $1,500.

3. A head of household taxpayer with modified AGI of $33,000 and Roth IRA contribution of $2,000.

4. A single taxpayer with modified AGI of $12,000 and an IRA contribution of $2,300.