Please can you check letter making it more natural Thanks a lot for your help

This is part of a letter from Jenny, your English- speaking pen-friend.
I’m getting ready for my A-levels at the moment. It’s rather difficult for me to remember all the necessary facts and figures. And when do you have exams in Russia? Do you find it easy to revise? Do you study at night? Is there any advice you could give me?
And another thing! My parents say you could come and visit us in summer. Would you like to? …
Write back to Jenny. In your letter-answer her questions
ask 3 questions about your trip to England

Dear Jenny,
Thank for your letter and I was so glad to receive a letter from you. How are things going? I hope your family is OK.
As for your questions, in Russia all school leavers must take two obligatory exams: math and Russian. Plus two other exams, but they are optional and students choose them themselves. These exams held every year in June.
The exams are very tough and needs everyday’s preparation. As for me, I try to revise what I have learned almost every day. I usually spend one hour on Math and half an hour on Russian. By the way, my optional exams are English and History. You know, I never study at night as I always follow Russian proverb which says it is better to do everything in the morning after rest. So I advise you to devote two three hour on revision. It is said that revision is the integral part of learning. I wish you good luck on your exams hoping you will manage to pass them.
Thanks for your invitation to England, it sounds great. Thanks. I would be happy to be your guest.
Now, let me ask you questions about my future trip. What should I wear? Do you live not far from London? What places of interest are there in your hometown?
I must go now to help my mum. I will write you soon and looking forward to your reply.
All the best,

TOEFL listening lectures: What is one way that Internet Addiction Disorder affects sleep?

Hi, sorry I did not know the UK usage of revision, but I trust you are correct in your letter. I thought this letter sounded great - I am having trouble finding any errors. By the way, what are these letters for? Is it practice for a test or for school or just to improve your English?