input: Write a python function to calculate the average of a list of numbers.
  assert calculateAverage([5, 10, 15, 20]) == 12.5
  assert calculateAverage([1, 2, 3, 4, 5]) == 3.0
  assert calculateAverage([10, 20, 30, 40, 50]) == 30.0
output: def calculateAverage(numbers):
      if not numbers:
          return 0
      return sum(numbers) / len(numbers)