13. On January 1, 2013, Barbara takes out a $12,000 loan, at an annual effective interest rate of 7.5%. Interest is being paid annually beginning on January 1, 2014. In addition, a sinking fund is established to repay the principal on January 1, 2022. Payments are made into the sinking fund annually, with the first payment on January 1, 2014, and the last payment on January 1, 2022. The sinking fund earns an effective annual interest rate of 4%. From Barbara's point of view, what rate of interest is she really paying each year