PreferredCustomer Class A retail store has a preferred customer plan where customers can earn discounts on all their purchases. The amount of a customers discount is determined by the amount of the customers cumulative purchases in the store, as follows: When a preferred customer spends $500, he or she gets a 5% discount on all future purchases. When a preferred customer spends $1,000, he or she gets a 6% discount on all future purchases. When a preferred customer spends $1,500, he or she gets a 7% discount on all future purchases. When a preferred customer spends $2,000 or more, he or she gets a 10% discount on all future purchases. Design a class named PreferredCustomer , which inherits from the Customer class you cre- ated in Programming Challenge 7. The PreferredCustomer class should have fields for the amount of the customers purchases and the customers discount level. Write one or more constructors and the appropriate mutator and accessor methods for the classs fields. Demonstrate the class in a simple program.