IX. Rewrite these sentences using the cues provided with SO/SUCH/TOO/ENOUGH

We went to bed early because we were very tired.
We were so tired that we went to bed early.

The lesson is very difficult. We can't understand it.   
The lesson is such a difficult lesson that we can't understand it.

The car is so old that he doesn't want to drive it.
It is such an old car that he doesn't want to drive it.