At the start of the question where Eric hasn't climbed down or up yet, he is considered to be at 0. So, by climbing directly downwards 2 and a half meters he is at -2 1/2 from his starting point, to get there from 0 you must subtract 2 1/2. Then he climbs up 6 3/4 meters. What point he is at is besides the point, but putting this on an equation he you will add 6 3/4. Then you can see that the equation in answer B makes the most sense. Hope this helps!
