You take out a loan to pay the remaining 15,000 on your car. The dealership gives you a monthly payment of 512 for 48 months. What is the dealers rate of return on this loan?

I have got a cash flow diagram set up and i was trying to use the present worth formula for even payment series to slove for interest. I tried plugging the values into Excell, IRR(values, guess), and got 2%. This is incorrect.

Any help would be great.

-Lance