英语翻译

1. The customers always grumble at the manager about the bad service in the restaurant.
2. It's impolite to tease at other people's weaknesses.
3. If I'm wrong, please correct me at once.
4. When I received his letter, he has already left Shanghai for Paris.
5. He failed because he lacked confidence.
6. I paid him 400,000 yuan for that apartment in the highrise.