Aaron seeks the help of a social worker for a problem he can no longer avoid. Recently, his employer downsized, and the client had to be placed on an afternoon shift to keep his job. Aaron does not own a vehicle and has always relied on public transportation to and from work. Because of his crippling fear of the subway system, Aaron takes the bus to work. With his new schedule, he must take a bus that gets him to work two hours early, while if he took the subway, he would be able to leave much later. Aaron is requesting help to overcome his fear of the subway system. The social worker suggests he observe others with the same fear. What form of therapy is most likely to be successful in this situation?