The correct answer is: A. Cash price remaining unpaid
Hire purchase is a type of installment purchase where the buyer agrees to pay the full price of the goods over a period of time, with interest. The interest is calculated on the cash price of the goods, and is payable on the amount that is still outstanding.
Option B is incorrect because the installment price is the total amount that the buyer will pay over the course of the agreement, including interest. The interest is not calculated on the installment price, but on the cash price.
Option C is incorrect because the amount that has been agreed under hire purchase agreement is the total amount that the buyer will pay over the course of the agreement, including interest. The interest is not calculated on this amount, but on the cash price.
Option D is incorrect because the cash price minus the amount of hire purchase installment paid is the amount of money that is still outstanding on the loan. The interest is calculated on the cash price, not on this amount.