Its actually $598.00-47.27 = 550.73 He had a negative balance in his account of $ 47.27 so the bank took out the difference from his deposit of $ 598.00 and it left him the balance of $ 550.73
I line that is perpendicular is a line with reversed slopes like 2/1 is perpendicular to -1/2. So find the slope by getting the y by itself and reverse it. Remember to switch the signs too! P.S. if you don't know how to get the y by itself just take and subtract 3x from -5y and -4 then divide by 5. Hope I helped!