A man holds a child on his shoulders while watching a football match.How much work has he done if the game lasts for 2 hours?

I expect the answer they want is zero, since the child has not moved.

Work = force * distance.

In fact, of course, his body has expended much chemical energy holding the child in place, eating hot dogs, spanking the squirming child, etc. But since no relevant data has been given to assess those requirements, I think a response of "zero work" will be accepted.