3. Understand that perpendicular equations' slopes are opposite and reciprocal to the original equation. The slope of the original equation is , so the reciprocal and opposite (flip and change the sign) slope would be .
Common rule of your salary => housing expenses + other debt payment should not be more than 36% of you monthly income. => 4 300 dollars is you monthly income. Let's solve the 36% of it => 4300 * .36 = 1548 => 1548 - 321 for you student loan = 1227 dollars - the housing expenses.