Answer:
20 N
Step-by-step explanation:
The question above is related to "Newton's Third Law of Motion." It states that every action is being opposed by a reaction of equal size but different direction.
The action force in the situation above is 20 N while the reaction force here is the one coming from the volleyball. So if the action force is 20 N then it's a common sense that the reaction force is also 20 N.
Thus, 20 N is the amount of force that the volleyball is exerting on Ana.