The Answer:
If Sandra started at 800 meters and went up 120, the answer would be 920.
Explanation:
First, simply add 800 meters, which is what she started with. Next, since she has gone up 120 meters since then, and the question is asking us what her elevation is NOW, you can add 800 + 120 to get 920. This question is solved by using addition.
Hope this helps!