this problem right here requires the understanding of displacement quite well. Now, in many physics problems there may be few numerics that you might have to know without their mention in the question. Just like that, to solve a problem with free falling, many a times you have to assume the acceleration is plus-minus 9.8 m/s. Just like that, in the above problem it is told that the orange returns to its initial position, and by the definition of displacement.
Displacement = change in the position. Thus we had to deduce that the displacement must be zero if its initial and final positions were the exact same positions. I hope this helps