Dear... (your friend's name),
I heard your mother said that you're experiencing a stress, so I wrote this letter to give you some advice on how to deal with the stress. I know you are going to finish your junior secondary school, and you're really nervous. Don't worry and believe yourself! That's the first thing you should do now. This will reduce your stress. Another advice for you is don't stay up late. Staying up late at night is really not good for your health and even for your nervous system. And the last, the easiet and the most effective thing is listening to music. You can listen to your favourite songs if you like. The music will make your brain relax, too.
Cheers,
...(your name)