Newton's Third law states that for every action there is an equal and opposite reaction.
The problem has two ice hockey players who are standing on ice; as the friction due to ice is very small it can be ignored.
The player weighing 100 kg pushes the player weighing 112 kg by a force equal to 50 N. This results in an equal force of 50 N exerted on the player weighing 100 kg by the player weighing 112 kg and in the opposite direction.
The force on both the players accelerates them in the direction of the force. The acceleration is given by Force/mass.
The player weighing 100 kg moves with an acceleration equal to 50/100 = 0.5 m/s^2. The other player weighing 112 kg is accelerated by 50/112 = 0.4464 m/s^2 in the opposite direction.