1. (20)  Add and implement two classes to the class hierarchy mentioned during
class.  Both classes should derive from Teacher.  The first is Professor, the
second is Instructor.  Professor adds the dateOfTenure member variable and 
associated member functions.  dateOfTenure should be a string of the form
"ddmmyyyy".  Instructor adds the semesterHired member variable and associated
member functions.  This should be a string of the form "Fall 2004" or 
something similar.