| When the roof was completed, there was 1/6+1/12+1/7=33/84 of the work. There was then 84/84-33/84=51/84 of work to be done. The floor took half of the time, which is 42/84, so that means that the windows, doors and the moat, which took 5+4=9 days took 51/84-42/84=9/84 of the time.
That means that the whole job took 84 days to get done. |