I am not sure what you are asking..... The INTEREST on a loan of $2500 if you have the loan for 9 months and the ANNUAL interest rate is 8% would be 2500 (.08)(9/12) = $150.00 (nine months of 12 month long year)
If you mean "how much interest would this loan cost you", then this is what you have to do:
1) You have to calculate a monthly payment for the loan, which comes to:$287.12
2)Then you multiply $287.12 x 9 months =$2,584.08
3)Then you subtract $2,584.08 -$2,500 =$84.08 interest - cost of the loan.