Q4: (5 Marks) Consider Black Friday Sale, where the customers can purchase the available items at discounted prices for a limited time. This flat discount scheme has a direct effect on the billing strategy of the stores. Every store has a different discount percentage on their items. Few stores offer 10% and some offer 20% discount on total billing amount (assuming these are the only two types of offers available at the moment). Define the appropriate class for the StoreSale along with the derived classes implementing the concept of pure virtual functions in order to calculate the bill of the purchased product. Keep in mind that different bills will be generated for stores offering 10% discount and stores offering 20% discount on their items