16. This is an exercise on syntax and mechanism; do not worry too much about style.
 The class X has a REAL attribute called number, a make routine, and three other routines. The first routine (set) receives the initial value of number as an argument. The second routine (add3) adds 3 to the number and displays the new value. The third routine (add) takes an integer as argument, adds this to number, and displays the new value.
 Hint: Code a routine header, then the routine body.