1) This question was discussed by us at the meeting
2) The conference is being watched by me online
3) The boy's exams have recently been passed by him
4) The rule was explained TO us by our teacher
5) The homework will be prepared by the children tomorrow
6) The rule is being explained to my friend by me(не очень звучит. это предложение не подходит для перевода в passive voice, но таково задание)
7) A new house has been built by a soldier recently