What was the hiker's total displacement?
a.24 km b.4 km north c.14 km northeast d.0 km

We can see it as two movements: one on the north-south axis and one on the west-east axis.

On the north-south Axis, the hiker went 8 km north and 4 km south, so in total the hiker went 4 km north (we can subtract one for the other and the direction remains that which was bigger)

On the west-easth Axis, the hiker went 6 km east and 6 km west, so in total the hiker  didn't move on this axis! or, he/she moved but then "came back"

So in total, the hiker only moved4 km north - answer B.