Assuming you are using the rule that housing shouldn't exceed 30% of income and that the mortgage payment includes taxes and insurance costs you want to take the following steps to determine the answer.
1248.90/x = 30/100
124,890/x = 30
124,890 = 30x
4,163 = x
$4,163/mo is the minimum amount you want in income per month to keep your housing expense in the acceptable range.
