I solved the Question 5, and I found the secret of this question.

We can know the general formula of the area is removed in each step. We treat the general formula as a series.Then the sum of the series is the area which has been removed. By the knowledge we have learned about the series. We can know the sum of this series when n approaches a large number which approaches to a constant.Then we know the Sierpinski carpet, and we can solve the question.

I think we need to transfer the questions to the knowledge we have learned.