Think of it like a graph. You start at the origin which is (0,0). go three to the east which now you are (3,0). Then, six to the north. Now, you are at (3,6). 1 to the east, ((4,6). Then you go 4 to the west which is back tracking. So, you end at (0,6) which is saying you are now 6 km north from your campsite.
Hope this helps!