The correct answer is A.
In the diagram, you are told that the ocean floor is 5km below sea level, and in the text below, it says that the ocean floor has an elevation of -5km. We can safely assume that the sea level is therefore 0km. (-5 + 5 = 0)
It also states that the summit is 10km above the ocean floor. If the ocean floor is -5km, and the summit is 10km, we can see that the elevation of the summit is 5km. (-5 + 10 = 5)