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.
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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