Dear Joan,
I know you are good at singing and want to become a professional singer. I'm writing this letter to you to give you some advice. I think you should become a professional singer because you can be famous and popular. You can enjoy singing and can earn a lot of money at the same time. However, if you want to be professional, you have to study hard and train yourself well. You also have to put in lots of effort. I hope you can be good singer in the future. (90字)