work at **
work on ***

Especially in the study, where he had worked at night.

More than 80 percent had worked at some point in the year.

He got out of bed and set to work right then, at three in the morning.

So more of the police worked at night, when needed.

He worked almost until his death at 93 in 1988.

Maybe one of them worked at the phone company or something.

"I understand she was working here at the time of her death."

Once she came in and found him working at his table.

But now, after six days, I began to work at the problem in my mind.

I did work a little while at first with the girl who had the job.