First, you add -3 to itself 7 times.
[tex] - 3 + - 3 + - 3 + - 3 + - 3 + - 3 + - 3 = - 21[/tex]
Then, add the distance he went to the distance he's already went.
[tex] - 21 + - 15 = - 36[/tex]
Do -96--36 to find how far he is from the ocean floor.
[tex] - 96 - - 36 = - 96 + 36 = - 60[/tex]
So, he is 60m from the ocean floor