To help you get started: Add together the monthly payments. Divide this sum by the given gross income. Here we'd get $1000/$4500, or 10/45, or 22.2%, and Tran's remaining income after debts would be $4500-$1000 = $3500.
You will have to review your class notes and/or textbook to determine "the largest piti for which he could qualify," based upon these figures.
