Which of the following equations can be used to find the internal rate of return (I) for a project that has an initial investment of P, net annual cash flows of A, and salvage value of S, after N years?
a) I = (A - P) / S
b) I = (P - A) / S
c) I = (A - P) / (P * N)
d) I = (A - P + S) / N