Tom, Dick and Harry piled stones into a pyramid to my precise specifications. Fred, an efficiency expert carefully watched them.

When the pyramid was complete, Fred reported that if Tom had worked twice as fast the job would have taken exactly 2 hours less, if Dick had worked three times as fast the job would have taken exactly 3 hours less, and if Harry had worked four times as fast the job would have taken exactly 4 hours less.

How long had the job taken?