I'm trying to set up a formula that will determine the last amount of cash flow in a stream of payments that is required to reach a certain return. For example, if I have these cash flows YR 0 -50,000,000, YR 1 4,922,955, YR 2 7,086,093, YR 3 8,486,159, I want a formula that will determine how much cash flow I need in YR 4 to achieve a 10% IRR. Any suggestions?