How do I count the number of people needed on a project over various days?

Schedule.xlsxSchedule.xlsxAttached is the spread sheet with the following problem:

You have jobs 1-10 which have overlapping days in duration (input duration is in hours). In column M, you are supposed to see the number of men required to work each day (as a cumulative of all projects). I cannot get the numbers to work out correctly. Can someone please help? The 'corect' numbers are calculated manually in column O

Thanks,

Eric.