Hello, Fat,
8 payments of $5 each means Bella gave the store $40, but it is not clear if this was payment on a prior purchase or a monthly deposite for future purchses. I'll assume they were deposits for future purchases. If she returns one game and receives $27, she has $27 in her purse and still $40 in credit with the store. So the change to the amount of money is $27.
Bob