I have issues with this problem.
 You have been given the Amortization Formula?
. . .And you're expected to manipulate it algebraically? . . . in Grade 9 ?
 I don't agree with their numbers.
$10,000 loan to be paid over 4 years.
Monthly Payments is: .
(a) Find the monthly payment when interest rate is 8.25%
(b) What interest rate would require a monthly payment of $255?
Amortization Formula: .
. . where: .
For the 8% loan, we have: .
So I don't trust the author(s) of this problem . . .