Поставьте глаголы в скобках в соответствующую форму, Не did not know

Поставьте глаголы в скобках в соответствующую форму, Не did not know that the boss (to sign) the contract last week. I am not sure, if I (to leave) Liberia next week. Did he say that he (to write) a letter yesterday at five? We decided that we (to agree) to their proposals. I heard that you (to telephone) our partners in London next Monday. We understood at once that the work (to be) a difficult one. When we ( to come) to the airport, the plane already (to land).