Can i get some answers to this to check my work ?

Simplify (a/b - b/a) times (a - a^2/a+b) a - a^2/a=b is a mixed number

Ricky takes out a $31,800 student loan to pay his expenses while he is in college. after graduation, he will begin making payments of $190.66 per month for the next 30 years to pay off the loan. how much more will ricky end up paying for the loan than the original value of $31,800? ricky will end up paying $ more than he borrowed to pay off the loan.

Can someone tell me if this is perpendicular? !