Chapter 10, Problem 1E

Create an application class named LetterDemo that instantiates objects of two classes named Letter and CertifiedLetter and that demonstrates all their methods. The classes are used by a company to keep track of letters they mail to clients. The Letter class includes auto-implemented properties for the name of the recipient and the date mailed. Also, include a ToString() method that overrides the Object class’s ToString() method and returns a string that contains the name of the class (using CetType and the Letter’s data field values. Create a child class named CertifiedLetter that includes an auto-implemented property that holds a tracking number for the letter.