Could I please get help with this question?? Just an explanation on how to do it please:)

Answer:
approximately 1584.9 m
Step-by-step explanation:
Add 3 parts together:
first part is the top dark line (1200-800)=400
The vertical line at the bottom (1100-900)=200
The slant will come from the pythagorean theorem using 400 and 900 as legs so find 400 squared + 900 squared =970000
Now take the squre root of that, approximately 984.9
Add 400+200+984.9=1584.9 m