Тут нужно раскрыть скобки и по всем временам simple
1. Dinner (be cooked) by mother. 2. This problem (be discussed) by the students. 3. A new grammar rule (be explained) by the teacher. 4. The poem (be learnt) by the pupils. 5. A beautiful piece of music (be played) by the pianist. 6. The suit (be made) by a tailor.