The best analysis is to compare side by side the after tax proceeds of the cash sale and then assume a theoretical rate of return on the reinvested proceeds i.e. 10%. And, compare that to the after tax proceeds of the installment sale over the duration of the installment proceeds received. The answer that you are trying to arrive to is which option provides the higher net present value, and secondly what rate of return do you need to earn on the cash option in order to outperform the installment sale option.