Here is a simplified version of your question. You pay $50/month for 3 months with 10% interest rate. Total Payment is$50*3 = $150. 3rd month $50 = X3 \times 1.1$$X3 = 50/1.1 = 45.45$ 2nd month $45.45+50 = 95.45 = X2\times1.1$$X2 = 95.45\div1.1=86.77$ 1st month $86.77+50 = 136.77 = X1$$X1 (AskingPrice) = 136.77$ 136.77 is the asking price. There should be$13.23 of interest to make $150.00. 45.45*0.1 + 86.77*0.1 = 4.55+8.68 =$13.23 .