For example, a candy bar item might cost 1.35 with a discount of 0.25 for preferred customers, meaning that preferred customers get it for 1.10. (some items will have no discount, 0.0.) currently the above classes do not consider discounts. every item in a bill is charged full price, and item discounts are ignored. define a class discountbill that extends grocerybill to compute discounts for preferred customers. the constructor for discountbill accepts a parameter for whether the customer should get the discount. your class should adjust the amount reported by gettotal for preferred customers. for example, if the total would have been $80 but a preferred customer is getting $20 in discounts, then gettotal should report the total as $60 for that customer. you should also keep track of how many items a customer is getting a non-zero discount for and the overall discount, both as a total amount and as a percentage of the original bill. include the extra methods below that allow a client to ask about the discount: