A syntesizer is advertised at $500 down and $100 per month for 18 months. If interest is charged at 18% per annum compounded monthly, what is the cash proce of the synthesizer?

hi guys, i need to know what does $500 down mean and how to calculate it.

I know it has something to do with the Annuity formula:

A = R[(1+i)^n -1] / i

thanks in advance!

Michael