(recommended project: combining composition and inheritance) in this chapter, we created the commissionemployee– inheritance hierarchy to model the relationship between two types of employees and how to calculate the earnings for each. another way to look at the problem is that commissionemployees and are each employees and that each has a different compensationmodel object. a compensationmodel would provide an earnings method. subclasses of compensationmodel would contain the details of a particular employee’s compensation: —for employees compensationmodel subclass would contain grosssales and commissionrate instance variables, and would define earnings to return grosssales * commissionrate.