Поставьте предложения в отрицательную форму. К выделенным словам поставьте специальные вопросы.

He grants us a 3% discount for cash payment.
You should have called your friend long ago.
He knew what was wrong with the machine.
The manager will be able to receive to Mr. A. only in the afternoon.
I had to sign this agreement only on Monday.
They have to transport their products by rail.
Participation in fairs helps promote our goods.

He doesn't grants us a 3% discount for cash payment. You don't should have called your friend long ago. He doesn't knew what was wrong with the machine. The manager doesn't will be able to receive to Mr. A. only in the afternoon. I  don'r had to sign this agreement only on Monday. They doesn't have to transport their products by rail. Participation in fairs doesn't helps promote our goods.