Answer: The player exerts 50N of force on the puck.
Explanation:
We are given that 70kg hockey player hits a puck of 0.1kg and after the collision, the puck exerts a force of 50N in the west direction.
According to Newton's Third law:
Every action has an equal and opposite reaction.
This statement means that if during a collision, one object is experiencing a force then another object will have same magnitude of force in opposite direction.
In the question, puck exerts a force of 50N and moves in west direction which means that the hockey player has exerted a force of 50N from east direction.