Calculate the average amount of interest paid on all three loans. You borrow $15000$ and replay the loan over $8$ years. At the end of each year, you make interest payment to the lender at an annual effective rate of $9\%$ and also make level payments to a sinking fund which accumulates to $15000$ after $8$ years. If your total annual payment is $2876\mathrm{.}65$ what effective annual rate is earned by the sinking fund?