A developer offers lots for sale at $60,000, $10,000 to be paid down and $10,000 to be paid at the end of each of the next five years with "no interest to be charged." In discussing a possible purchase, you find that you can get the same lot for $48,959 cash. You also find that on a time purchase there will be a service charge of $2,000 at the date of purchase to cover legal and handling expenses and the like. Approximately what rate of interest before income taxes will actually be paid if the lot is purchased on this time payment plan?