Please help with grade9 Math-Linear/NonLinear Equations on how to compute for loans, monthly repayments and interest rates.

$10,000 loan to be paid over 4 years at various interest rates:

Monthly Payments is $242.51 for interest rate of 8%

$244.75 for interest rate of 8.5 %

Question: Find the monthly payment when interest rate is 8.25%

What interest rate would require a monthly payment of $255?

Appreciate your kind help.