A person is pushing against a couch with a force of 50 n. what is the force of the couch against the man if the couch does not move?

Newton's third law of motion states that for every applied force, there is an equal and opposite reaction force.

Therefore if a person pushes against a couch with a force of 50 N, the reactionary force from the couch against the man will be 50 N.

Because these forces are equal and opposite, both the couch and the person will remain in static equilibrium.