The answer is zero. As a hole, the area contains no dirt. If it did, it wouldn't be a hole anymore. If you mean how much dirt was displaced in digging the hole in the first place, that's something different.
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Calculating the volume of an area is simple enough if we have the length, width and depth of the area concerned. The formula is as follows:
Volume = length x width x area.
In this instance, we have:
Volume = (4 feet x 3 feet) x 5 feet.
Volume = 12 feet x 5 feet
Volume of the hole/displaced dirt is therefore 60 feet cubed.
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