If I'm reading this question correctly, the question is asking how many more hours should the men work to get the work done in 4 days assuming they work at the same pace as they did for the first 5 days.

I'm going to make the assumption that each man works the same amount. Over the course of 5 days, each man worked 8 hours per day or a total of 40 hours. In 40 hours of work per man, they completed 40% of the work. Therefore to complete the remaining 60% of the work, they have to complete 60 more hours of work.

60 hours spread across 4 days is an average of 15 hours per day.

The answer is E - 15 hours

@cappyaa
Its said that they initially take 9 days to complete a work. So as per this by the 5th days end they should obviously have completed more than 50% of the work. Now if the problem says that after the 5th day they've only completed 40% it means that there was some other unforeseen delay which caused a lesser amount of work to be done. So we can't assume the rate to be based on the work done in these 5 days. Whats ur opinion?

That's why I think there is something missing with the wording of the problem. There needs to be another sentence in the question so you know what rate to use.

If you assume the original rate (72 hours to complete the work), after finishing 40%, they'd have completed 28.8 hours worth of work and will have 43.2 hours worth of work left to complete in 4 days. This would leave 10.8 hours of work per day left, which is not an answer choice.

I still do think we're supposed to assume that their rate is not as fast as originally said, but I agree that it's a poorly worded question.

Yes, the wording makes no sense.

64 men can complete a work in 9 days working for 8 hrs a day.

Apparently they can't...

how many hours should the men work in the remaining 4 days so that they finish the work by the 9th day

Well the OA is 15, so I am assuming that people do not work at the rate that was mentioned and hence failed to do work.

And as CappyAA mentioned, if they continue to work at their new rate(slower), it would take them 60hrs or 15 hrs a day to complete the work.

Terribly worded problem though.