3 km north
Just add the vectors together. Consider north to be positive, south to be negative, west to be positive, and east to be negative. Just remember to keep north/south and east/west separate from each other. So let's start with 0 north, 0 west.
Add 5 km north. So 0 + 5 = 5, giving us 5 north, 0 west.
Add 3 km east. So 0 - 3 = -3, giving us 5 north, -3 west (or 3 east).
Add 2 km south. So 5 - 2 = 3, giving us 3 north, -3 west (or 3 east)
Add 3 km west. So -3 + 3 = 0, giving us 3 north, 0 west
We can ignore the 0 west, and as a result we're 3 km north of where we originally started. So the total displacement is "3 km north"