请用下面格式：
Dear mum and dad ,
……
Bingbing
范文：
Dear mum and dad ,
I'm afraid I have to go home late today , because we have a new classmate . He is very poor in maths and English , so I need to help him to catch up with the class after school . We will stay at school for about an hour . I will get home at about six .
Bingbing