The first payment of a constant perpetual annual cash flow is received at time 5. Let this cash flow be C5 and the required return be r.
So there will be equal annual cash flows at time 5, 6, 7 and so on forever, and all of the cash flows will be equal so C5=C6=C7=...
When the perpetuity formula is used to value this stream of cash flows, it will give a value (V) at time: