If you invest $4900 today at i (4) you will be able to withdraw $3000 in 2.5 years and $5000 in 7 years (after which you will have $0 left). Use linear interpolation between either 8% and 9% or between 9% and 10% (all rates are i (4) ) to determine the value of i (4). Then calculate the equivalent i (12) .