Since the shark is in a deep water level of specifically 80 feet it is then represented by a negative coefficient. This is due to the vector quantity the measure represents as decelerating or sinking or downward in direction. As oppose the shark moves upward with a height of 15ft.
Thus the expression will be -80ft + 15 ft = -65ft is the displacement.
15ft is positive since the movement is upward and the displacement then from the origin to the point of last position is 65ft, negative.
