For a better understanding of the solution provided here please find the diagram in the file that has been attached. As shown in the diagram, the sea level is taken as the "zero level" thus making 35 feet below sea level as -35 and making 2 feet above (or in the air) as +2 (or simply 2).
The fish was at P1 (35 feet below sea level or, -35) to start with and jumped to P2 (2 feet above sea level, or 2), so the total distance travelled by the fish is the distance between the positions of P1 and P2 which can be shown as:
feet.
Therefore, the fish travelled a total of 37 feet from it's previous position which was 35 feet below the sea level.
