NPER(rate, PMT, PV, FV, type). Returns the number of periods for an investment based on periodic,constant payments and a constant interest rate.
* Rate is the periodic interest rate.
* PMT is the constant annuity paid in each period.
* PV is the present value (cash value) in a sequence of payments.
* FV (optional) is the future value, which is reached at the end of the last period.
* Type (optional) defines whether the payment is due at the beginning (1) or the end (0) of a period.