3. Create two classes, Patient and Billing, whose objects are records for a clinic. Patient will be derived from the class Person. A Patient record has patient ID and primary physician of type Doctor, in addition to the inherited properties. A Billing object will contain a Patient object, a Doctor object, and an amount of type double Be sure your classes have a reasonable complement of constructors, accessor, and mutator methods, and suitably defined display methods Write a test program that creates at least two patients, at least two doctors, and at least two Billing records, and then prints out the total income from the Billing records. Detail of Classes: Person: Name, Gender, Age Doctor: Doctor ID, Specialization. (Inherited from Person)