Net displacement is the distance of a straight line from the beginning point to the end point.

You can walk what would be a straight path of 2 km or a 12 km scenic path and both lead to the same point. You decide to take the scenic route and walk for 12 km to your destination.

Your net displacement is only 2 km even though you chose to walk the 12 km path, because it's the shortest distance between the start and finish points.

To solve this problem it looks like you're going to have to find the hypotenuse of a triangle. If you draw the paths on a sheet of paper you can draw a straight line north from where he started 40 m distant.

Next you can draw a diagonal line at an angle toward where he ended his run from the beginning point.