Dear Svetlana Ivanovna,
Thank you for your letter. How are you? I am fine.
(Тут текст должен быть тот, на какую тему)
(Дальше 3 вопроса по теме. Например, если тема спорт, то спрашивайте так: And what sport do you like best of all? How often do you do this sport? What sport dont you like?
Hope to here from you soon.
Yours,
(Имя ваше).