15. The interest rate on a four-year fund varies from year to year, as follows: (i) During year 1, the fund earns an effective annual rate of 5%. (ii) During year 2, the fund earns a nominal annual rate of 7%, convertible quarterly. (iii) During year 3, the fund earns a nominal annual rate of 6%, convertible semiannually. (iv) During year 4, the fund earns a nominal annual rate of 10%, convertible every two years. Find the effective annual rate of interest over the four-year period