完形填空。

    Hello, I am John. Look, this is a picture 1my room. I have a nice bed in the middle of my room. There is a big table 2 the closet and the bed. Many clothes are 3 the closet. A white air-conditioner is4 the wall beside the window. There is a computer on the table. I often write e-mails with it.

    Do you like my room? What's your room 5? Can you tell me, please?

一条弧所对的圆心角为135°，弧长等于半径为5cm的圆的周长的3倍，则这条弧的半径为____ 。