new_contents: #!/usr/bin/env python
  
  # Exercise 21: Functions Can Return Something
  
  def add(a, b):
      print "ADDING %d + %d" % (a, b)
      return a + b
  
  def subtract(a, b):
      print "SUBTRACTING %d - %d" % (a, b)
      return a - b
  
  def multiply(a, b):
      print "MULTIPLYING %d * %d" % (a, b)
      return a * b
  
  def divide(a, b):
      print "DIVIDING %d / %d" % (a, b)
      return a / b
  
  
  print "Let's do some math with just functions!"
  
  age = add(30, 5)
  height = subtract(78, 4)
  weight = multiply(90, 2)
  iq = divide(100, 2)
  
  print "Age: %d, Height: %d, Weight: %d, IQ: %d" % (age, height, weight, iq)
  
  
  # A puzzle for the extra credit, type it in anyway.
  print "Here is a puzzle."
  
  what = add(age, subtract(height, multiply(weight, divide(iq, 2))))
  
  print "That becomes: ", what, "Can you do it by hand?"
  
subject: add ex21