in these cases we should be convert the total work as man hour
here 6 men take 10 hr to complete work
hence the work need total 6*10=60 man-hour to complete
now if we divide this man-hour with available number of men we will get the result
in the example 6 men worked from 11am to 5pm i.e 6hr
so
no of Men Hr work done(in man hr)
6 11am 0
6 5pm 36
7 6pm 43
8 7pm 51
9 8pm 60

so ans is 8 pm the work will be done
let me know if this helps .

Yes, thank you very much. Very staightforward approach and quite understandable.

In other words, 60 man per hours means the "total work" to be done?

Thanks again. your response was very quick.

If I may, I would like to ask you for a general advice on Work Problems, because I find it to be my weak area at the moment and I want to focus on it, so your advice on dealing with any Work Problem would come very handy.

work problems can be solved mostly with the concept of man hour some times the calculation of man hour might not be straight forward..you can apply this concept to solve more similar problems to understand the concept better.
If you are stuck with any specific issue you can post here .

thanks.