Hi aspirant,

Since the farmer covers 10 m in 4 seconds The distance travelled by him in 2 minutes 20 seconds that is equal to 140 seconds is equal to 10/4 X 140= 350 meters. Now after covering every 40 m he is back to his original position therefore after 140 seconds he would be 30 metres away from its original position but it is the distance. Since the displacement is the smallest path between the two points the displacement would be 10 m.

Hope it helps!