First, I assumed that the interest rate of 88% is actually 8%. Based on that, the monthly payment is
=$243.32.
$243.32 x 60 months =$14,599.20 total interest plus principal.
$14,599.20 - $12,000 =$3,599.20 total interest on the loan over 5 years.
This is how calculate your monthly payment:
PMT = 12,000(.08/12) / [1 - [1 + 0.08/12]^-(5*12)]
PMT = 80 / 0.3287896
PMT = $243.32