Answer:
For the return, i guess that you say in the interval between 15:40 and 15:45, that is the moment where he goes back to his home, and pass through the local shop.
Ok, in the graph we can see pairs (time, position)
The average speed can be obtained with two of these pairs, and the average speed is:
As = (position2 - position1)/(time2 - time1)
In this particular case, we have the pairs:
(15:40, 900m) and (15:45, 400m)
(i guess that the distance is in meters)
Then the average speed is:
As = (900m - 400m)/(15:45 - 15:40)
and 15:45 - 15:40 = 0.5 minutes.
As= 500m/5 min = 100 m/min
This means that the average speed in this return is 100 meters per minute
