A retail store has a preferred customer plan where customers may earn discounts on all their purchases, the amount of a customer’s discounts is determined by the amount of the customer's cumulative purchases in the store.

- When a preferred customer spends $500, he or she gets a 5% discount on all future purchases.

- When a preferred customer spends $1000, he or she gets a 6% discount on all future purchases.

- When a preferred customer spends $1500, he or she gets a 7% discount on all future purchases.

- When a preferred customer spends $2000 or more, he or she gets a 10% discount on all future purchases.

Design a class named Preferred Customer, which is derived from the Customer Data class you created and should have the following member variables: purchases Amount (a double), discount Level (a double).

The purchase Amount variable holds the total of a customers purchases to date. The discount-Level variable should be set to the correct discount percentage, according to the store's preferred customer plan. Write appropriate member functions for this class and demonstrate it in a simple program.