Dora purchases a ten-year decreasing annuity-immediate, with annual payments of 10,9,8,....,1. Diego purchases a perpetuity-immediate with annual payments 1 in year 1, 2 in year 2, 3 in year 3,.... , and 11 in year 11. After year 11, the payments remain constant at 11. At an effective annual interest rate of i, the present value of Diego's annuity is twice the present value pf Dora's annuity. Calculate the present value of Dora's annuity.