I have to create the classes in the inheritance hierarchy of the figure below. An Employee should have a first name, last name and social-security number. In addition, a SalariedEmploye e should have a weekly salary; an HourlyEmployee should have a wage and a number of hours worked; a CommissionEmplo yee should have a commission rate and gross sales. Each class should have appropriate constructors, set methods and get methods. Write a program that...