Lease Payment Calculation

Hello,
I'm trying to figure out a lease payment for a client of mine. I am leasing them equipment for 3 years, with a present value of $27,023, a residual value of $1, and a 15% rate of return. That part is simple, but I'm trying to account for the 8% cost of money to me. I'm getting that $27,023 from an investor expecting an 8% return. I am charging my client a 15% return and I make my money on the 7% margin. How can I calculate my client's payment using Microsoft Excel?
Thanks.

Maybe I'm missing something, but if you're charging 15%, how does what you're being charged affect the client? You have your principal, which you're being charged interest for, and loaning to your client for more. Your margin is the difference in payment between your client on the 15% and you on the 8%.