calculate the monthly payment by loan amortization table: loan $26,000; down payment $5,000; 11% 36 months

present value of debt = payment(1 - (1+i)^-n)/i

where i = monthly rate
n = number of months

i = .11/12 = .00916666..
n = 36

21000 = paym (1 - 1.00916666..^-36 )/.0091666..
paym = $ 687.51