Sure! Here are the rewritten sentences in reported speech:

1. **“Where does your father work?”**
→ The teacher asked me where my father worked.

2. **“How many people are there in your family?”**
→ He asked Lan how many people there were in her family.

3. **“How long will you stay in England?”**
→ Tam's friend asked him how long he would stay in England.

4. **“How do you go to the airport?”**
→ His friend asked him how he went to the airport.

5. **“How much does this dress cost?”**
→ Lam asked Lien how much that dress cost.

6. **“How often do you wash your clothes?”**
→ Ba asked Tam how often she washed her clothes.

7. **“When will your father leave Vietnam for the USA?”**
→ Phong asked Thu when her father would leave Vietnam for the USA.

8. **“How many books do the students need?”**
→ The librarian asked me how many books the students needed.

9. **“Have you prepared for the test next month?”**
→ The teacher asked me whether I had prepared for the test next month.

10. **“What have you prepared for the test next month?”**
→ The teacher asked me what I had prepared for the test next month.

11. **“Have you been standing there since two p.m.?”**
→ He asked her if she had been standing there since two p.m.

12. **“Are you still standing there, Mai?”**
→ He asked Mai if she was still standing there.

13. **“Why are you still standing here, Mai?”**
→ He wanted to know why she was still standing there.

14. **“We will wait here till you come back, Sir,” they said.**
→ They said they would wait there until the Sir came back.