Payments of $1800 and $2400 were made on a $10,000 variable-rate loan 18 and 30 months after

Question:

Payments of $1800 and $2400 were made on a $10,000 variable-rate loan 18 and 30 months after the date of the loan. The interest rate was 11.5% compounded semiannually for the first two years and 10.74% compounded monthly there- after. What amount was owed on the loan after three years?