input: Write a python function to find the maximum element in a list of numbers.
  assert find_max([1, 43, 78, 3, 92, 42]) == 92
  assert find_max([10, 20, 30, 40, 50]) == 50
  assert find_max([-1, -5, -3, -4]) == -1
output: def find_max(numbers):
      if not numbers:
          return None
      max_number = numbers[0]
      for num in numbers:
          if num > max_number:
              max_number = num
      return max_number