A loan of $20,000 is being paid by installments of $1,000 at the end of each six-month period and a smaller final payment made half a year later after the last regular payment. The interest rate for the loan is a nominal interest rate of 6% convertible semiannually. Find the outstanding loan balance when the borrower has made payments equal to 75% of the original amount of the loan. The answer is $12560.43 but can't figure out the steps to get there