Demonstrate how a class hierarchy is to be created containing the following classes:

• An employee having first name, last name and social security number
• A salaried employee having a monthly salary
• A commission employee having monthly total sales and commission rate
• Bases on the above information, devise a suitable class hierarchy to model the presented employees. You should also clearly identify which data items each object will store and the likely methods. Finally, you should also justify your design decisions. Write a program to implement the design.