A line of thought for this type of question goes like this. Depending on what type of repayments they make you do.
Annual repayments amount times no. of years
Monthly repayments amount times 12 times no. of years
Quarterly repayments amount times 4 times no. of years
Fortnightly repayments amount times 26 times no. of years
Weekly repayments amount times 52 times no. of years
Daily repayments amount times 365 times no. of years
For all of them take away the sale price will be the total amount of repayments.
*Bold can happen but rarely get used in exam questions
The main point of these questions is to convert the type of repayment into years, the main form of measurement.
Knowing this a and c should be trivial. That is why knowing maths is important so you do not get taken advantage of by loaners as CM_tutor said.