Final answer:
Without the discount rate or amount, it is impossible to determine the sale price of the backpack from the options provided.
Step-by-step explanation:
The question does not provide enough information to determine the sale price of the backpack. Usually, when items go on sale, they are offered at a discounted price from their original, or usual price. Since the given usual price of the backpack is $30.00, the sale price would typically be lower than that. Without knowing the discount rate or amount, we cannot accurately choose between options (a) $4.50, (b) $25.50, (d) $35.50, or confirm that it remains the same (c) $30.00 as the sale price. To find the sale price, you would need to know the percentage or amount of the discount being applied to the original price.