Answer:
16km
Step-by-step explanation:
Since its a right angle triangle we can use the pythogorean theorem, which is a^2 + b^2 = c^2
So if we apply it to this situation we get,
12^2 + b^2 = 20^2
144 + b^2 = 400
b^2= 400 - 144
b^2= 256
b= 16
So the answer is 16km
Hope this helped :)
