James and Steve were busily emptying their book shelves from one room to another.
James on his own could have cleared the room in 18 hours.
Steve also would take 18 hours.
Unfortunately, John was moving the books back into the first room from the second.
He could fill the first room in 36 hours.
How long will it take the three of them to complete the task?
[Ref: ZTUW] © Kevin Stone
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