If your monthly net (after-tax) income is $1,500, what should be your maximum amount spent on credit payments? a. $200 b. $300 c. $400 d. $500

There are rules for personal finance, and one of them may tell you a recommended limit to credit card payments when your net monthly income is a certain amount.  As such, this is not really a math question, but one in personal finance / economics.  Reread the original question and the instructional material that preceeds it and look for "max payments" guidelines.