URGENT! Need simplified explanation on how a mathematical problem is calculated

Hello - I need this solution within a few hours. Thank you.

This is the problem:
"Based on language in the Higher Education Act, which says for students to qualify for federal student aid, institutions must prepare them for "gainful employment in a recognized occupation." Under the new rule, a program would comply with that requirement if the annual loan payment of a typical graduate did not exceed 20% of his or her discretionary income or 8% of total earnings.

A student graduating with a bachelor's degree in 2012 with the average $29,400 in debt would need to earn at least $36,000 a year, assuming a 5.5% interest rate and a 15-year repayment schedule."

MY QUESTION - how does one calculate that the student with the average $29,400 in debt would need to earn at least $36,000 a year, assuming a 5.5% interest rate and a 15-year repayment schedule? What is the formula?

Thank you!