The first thing to consider is that when computing the APR for one month you must divide the interest rate by 12 since the 13.5% is based annually. 13.5% is equivalent to .135 in decimal form. But then when we divide it by 12 we get, (.135)/12 = .01125 which is your monthly interest rate versus your annual one. When multiplied by the amount of the cash advance you come up with the following fee:
(principle)(monthly int. rate) = total interest charged for month
($2,790)(.01125) = $31.3875
The next thing to consider is the additional charge of the 3.5%. This is equivalent to .035 in decimal form. When multiplied by the amount of the cash advance you come up with the following fee:
(principle)(advance int. fee) = total cash advance fee
($2790)(.035) = $97.65
So the total amount due at the end of the month would be $2790 + $31.39 + $97.65 = $2919.04 after interest rates and the additional fee gets applied.
