You can put this solution on YOUR website! Well, to be honest, if it is a hole then there isn't any dirt in it, so if the teacher is trying to be funny, or you want to be (be polite) then this could be a good answer to give.
However if you want to know how much dirt would fill the hole, or has been taken out of the space then you have to treat the hole area as a three-dimensional rectangle.
The volume would be height x width x length = 2 x 4 x 5
=