The man said, "I am going twice as deep," not "as deep again." That is
to say, he was still going twice as deep as he had gone already, so that
when finished the hole would be three times its present depth. Then the
answer is that at present the hole is 3 ft. 6 in. deep and the man 2 ft.
4 in. above ground. When completed the hole will be 10 ft. 6 in. deep,
and therefore the man will then be 4 ft. 8 in. below the surface, or
twice the distance that he is now above ground.