I can't take on any extra work.

我不能承担任何额外工作。

He was doubtful about accepting extra work.

他拿不定主意是否接受额外工作。

All this extra work is getting on top of him.

这么多的额外工作快使他吃不消了。

The conference is going to be a lot of extra work.

这次会议将意味着很多额外工作。

You have involved me in a great deal of extra work.

你害得我添了一大堆额外的工作。