def add(a, b)
  puts "Adding #{a} + #{b}"
  a + b
end

def subtract(a, b)
  puts "Subtracting #{a} - #{b}"
  a - b
end

def multiply(a, b)
  puts "Multiplying #{a} * #{b}"
  a * b
end

def divide(a, b)
  puts "Dividing #{a} / #{b}"
  a / b
end

puts "Let's do some math with just functions!"

age = add(30, 5)
height = subtract(78, 4)
weight = multiply(90, 2)
iq = divide(100, 2)

puts "Age: #{age}, Height: #{height}, Weight: #{weight}, IQ: #{iq}"

# A puzzle for the extra credit, type it in anyway.
puts "Here is a puzzle."

what = add(age, subtract(height, multiply(weight, divide(iq, 2))))
puts "That becomes: #{what}. Can you do it by hand?"