Đáp án + giải thích :  

6. She said that she wouldn't buy that car because it was very old.

Cách chuyển : I -> She ,  will -> would  ; this -> that  , thì hiện tại đơn -> QK đơn 

7. The teacher asked long how old he was.

Thì hiện tại đơn -> QK đơn ( are -> was)

8. Mrs White asked him how he went to his school. 

Thì hiện tại đơn -> QK đơn ( go -> went) 

Chuyển chủ ngữ you -> he 

Chuyển tính từ sở hữu : your -> his

9. Jonh said to his mother that he didn't know how to do that exercise.

Thì hiện tại đơn -> QK đơn ( don't -> didn't),chuyển this -> that.

10. He told me to go to the zoo. 

Câu đề nghị : S + told sb + (not) to V + ...