Change the voice of modals

Dear student,

5. Your brother should have been helped by you when he needed it.
6. This race ought to be won by you, you have worked hard for it.
7. The whole system might be disturbed by what you are doing.
8. The pay scales may be revised by us shortly.
9. The noise of the drums could be heard by us from a distance.
10. Why couldn't the building be completed by you in the stipulated time?

Regards