The answer is C. If we want to go on x rides, we need to pay 40+5x dollars at Thrill Park, and 60+3x dollars at Splash Park. The average money needed for each ride is (40+5x)/x at Thrill Park, (60+3x)/x at Splash Park. Therefore, the system of equations is y=(40+5x)/x, and y=(60+3x)/x.