A constant perpetuity with cash flow, C, will have the first cash flow occur exactly 20 years from now. Each subsequent cash flow will be exactly 4 years after the prior cash flow. You have used the formuls, PV=C/r (correctly) to determine a value. The determined value needs to be discounted exactly how many years to get the PV today of the cash flows? The determined value needs to be discounted exactly years to get the PV today of the cash flows