To solve for the interest rate the formula is. In Excel the PMTfunction returns the payment amount for a loan based on an interest rate and a constant payment schedule. For a more complete description of the arguments in PMT see the PV function.
I already have the syntax of the RATE function from the Excel help screen.
Number_paymentsis the number of payments for the loan. Interest is charged at a rate of 5 per year and the loan payments are made at the end of each month. The interest rate for the loan. You can use the PMT function to figure out payments for a loan given the loan amount number of periods and interest rate.