Sure, here are the sentences changed from active to passive voice:

4. Customers are served by waitresses and waiters.
6. A new idea has been suggested by Shirley.
7. The farmer's wagon was being pulled by two horses.
8. The book had been returned to the library by Kathy.
9. Will your house be painted by Mr. Brown?
10. I won't be fooled by his tricks.
11. The lesson is going to be explained by the teacher.