input: Write a function to find the maximum of three numbers.
  assert maximumOfThreeNumbers(10, 5, 20) == 20
  assert maximumOfThreeNumbers(30, 25, 15) == 30
  assert maximumOfThreeNumbers(7, 14, 7) == 14
output: def maximumOfThreeNumbers(a, b, c):
      return max(a, b, c)