Помогите с инглиш! Нужно преобразовать в страдательный залог предложения!

The letter was typed an hour ago.Our exercises were corrected.All the freshmen were greeted at the lecture.The letter wasn`t posted yesterday.Such things weren`t forgotten. A message for me will be left by them.Ann won`t be told about it. By whom was America discovered?By whom was this concert given?When was Moscow University founded by Lomonosov?What questions will be discussed at tomorrow`s meeting?The work can be finished in three days.These books must be returned to the library.