input: Write a python function to create a model that multiplies each input by 2.
  assert pred_model([1, 2, 3]) == [2, 4, 6]
  assert pred_model([4, 5, 6]) == [8, 10, 12]
  assert pred_model([0, -1, -2]) == [0, -2, -4]
output: def pred_model(inputs):
      return [x * 2 for x in inputs]