Answer:
Negative reinforcement
Explanation:
In psychology, negative reinforcement is a type of classical conditioning and therefore, a type of learning by which the individual strengths a certain behavior by removing a negative stimuli that occurs when the behavior is not taking place.
In this example, Eva is feeling constant anxiety but she starts playing Tetris and her anxiety is removed and when she stops, it comes back. The playing of Tetris is being reinforced because it helps Eva remove a negative stimulus (the anxiety) that occurs when she is not playing. Therefore, she ends up playing Tetris through the mechanism of negative reinforcement.