Attached is the loan formula solved for monthly payment.
This formula CANNOT be solved for rate. The rate can only be solved by trial and error by using different values for rate. I wrote a calculator which does this www.1728.com/calcloan.htm
To use the calculator, you will need to know the monthly payment which would be 10,320 / 48 months = $215.00 per month.
The rate is 13.095%
