Simple solution: Build 3 Vectors
[input](40, 0)[/input] for 40 meters east
[input](-20, 0)[/input] for 20 meters west
and
[input](0, -10)[/input] for 10 meters south
Now summarize these vectors and calculate the magnitude:
[input]len((40, 0)+(-20, 0)+(0, -10))[/input]
+104 
