Displacement and velocity

How does the teacher want those values presented? Both of those require magnitude and direction. You have the magnitude, you just need the direction. Is the teacher asking for an angle?

Engineer is pointing you in the right direction.... let me lead you a little further.

1. You are going to want to draw a picture.
2. I will give you a hint: You calculated the displacement incorrectly
3. I will give you a bigger hint: Pythagorean theorem.
4. The average speed is not going to be the same as the value of the average velocity. The speed is 7.29 km/hr. The average velocity have a lower value than that (if you look at the picture you drew, you will understand why).

When I was teaching, we used the term "tip to tail" when we taught students how to add vectors. I suspect that you either have heard that phrase, or you are about to. It is a very important concept in Physics.