Joshua is a songwriter who collects royalties on his songs whenever they are played in a commercial or a movie. Joshua will earn $30 every time one of his songs is played in a commercial and he will earn $120 every time one of his songs is played in a movie. Joshua's songs were played on 4 more commercials than movies, and his total earnings on the royalties from all commercials and movies was $420. Determine the number of commercials and the number of movies on which joshua's songs were played.
