What is the displacement for a driver who travels 10 km to get to a point that is 4 km from his starting point?

The displacement is the shortest path which is final point minus initial point.It is a vector quantity which has magnitude and direction.

Distance is the path travelled  is a scalar quantity.

Here, Say A is the starting point and He has covered total 10 km which is 4 km from the initial point

Hence, Displacement is 4 km which is the difference of final and initial point.

b.transmitters send radio waves, and receivers capture radio waves.

a longitudinal wave moves energy that is to the direction of the wave’s movement. - true