input: Write a python function to calculate the volume of a pyramid given its base side length and height.
  assert volume_pyramid(4, 6) == 128.0
  assert volume_pyramid(3, 9) == 108.0
  assert volume_pyramid(5, 10) == 333.3333333333333
output: def volume_pyramid(base_side_length, height):
      return (1/3) * (base_side_length ** 2) * height