1. Which time do your classes finish?

=>What time do your classes finish?

2. Our summer vacation last for about three months.

=> Our summer vacation lasts for about three months.

3. I think we have few vacations than American pupils.

=> I think we have fewer vacations than American pupils.

4. Our cows produce little milk than Mr. Tuan's.

=> Our cows produce less milk than Mr. Tuan's.

5. How much hours a day do you do your homework?

=>How many hours a day do you do your homework?