Question

A dog runs 50 meters north 40 meters east and 20 meters south what is the displacement

Answer 1

so....
imagine the x and y axis or draw it on a piece of paper, a white board or even on your wall if you like. I'm kidding just draw it on a piece of paper

50m up and 20m down 
the dog's displacement is 50 - 20 which is 30
your answer is 30m north