Adrian is a songwriter who collects royalties on his songs whenever they are played in a commercial or a movie. Adrian will earn $40 every time one of his songs is played in a commercial and he will earn $110 every time one of his songs is played in a movie. Adrian earned a total of $500 in royalties on 9 commercials and movies. Write a system of equations that could be used to determine the number of commercials and the number of movies on which Adrian's songs were played. Define the variables that you used to write the system.