??

Alex and Billie were busily emptying their book shelves from one room to another.

Alex on their own could have cleared the room in 18 hours.

Billie also would take 18 hours.

Unfortunately, Drew was moving the books back into the first room from the second.

They could fill the first room in 36 hours.

How long will it take the three of them to complete the task?

Puzzle Copyright © Kevin Stone

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Hint

How many rooms could Alex clear in 36 hours?

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