At first you need to know total cost

According to the fact that you have already paid for 7 months, we have to substract

---> what still needs to be payid.
On the 8 moth you have missed the payment so (218.75)(8/12), and remaining moths are nearly
145.83333
To finish, multiply by the apr and you will get $20.78 interest charged. So, I am pretty sure that he answer is D.