APR formula = (Finance charges/total balance) x 365
Purchase price = $3,900
Downpayment = $1,000
Total financed = $2,900
Payments (36m) = $100.53
Total amount = $3,619.08
APR formula = (Finance charges/total balance) x 365
APR = ($3619.08/2900) x 365
APR = 4.5%