There is 98.17477042 cubic feet of dirt in a 5 foot deep hole that is 5 foot across.
none
a lot of dirt.
6 cubic square
None, it's a hole! (1 cubic foot has been dug out.)
There's no dirt in a hole.
none, a hole has nothing in it
6 x 6 x 4 = 144 cubic feet
none, it is a hole
6 inches
All of it
10 fathoms is roughly 60 foot deep as 1 fathom is about 6 foot