6,“These old buildings might have already disappeared by the time I am back next year?” he said

---> he said those old  buldings might have already dissapeared by the time he was back the following year.

7. The boy said to the old woman: “What can we do to help you?”

--->The boys asked the old woman what they could do to help her.

8. The guests said to the doorman: “Where should we leave our coats?”

--->The guests asked the doorman where they should leave their coats.

9. Tom asked his brother: “Why did you advise them to go sight-seeing on foot?”

--->Tom asked his brother why he had advised them to go sight-seeing on foot.

10. I asked the children: “Who took away the magazines from my desk?”

--->I asked the children who had taken away the magazines from my desk.