input: Write a python function to cube each number in a list and print them.
  assert cube_numbers([1, 2, 3]) == [1, 8, 27]
  assert cube_numbers([4, 5, 6]) == [64, 125, 216]
  assert cube_numbers([7, 8]) == [343, 512]
output: def cube_numbers(lst):
      return [x**3 for x in lst]