Nick borrows a 15 year loan, which is repaid with annual payments at the end of each year. He repays the loan by making payments which are equal to X during the years 1-5, 3X during years 6-10, and 2X during years 11-15. Interest is charged on the loan at an annual effective rate of i,i>0. The amount of interest repaid during year 6 is twice as much as the amount of interest repaid during year 11. Calculate i. 4