Charlie does a weekly exercise program consisting of cardiovascular work and weight training. Each week, he exercises for at least 9 hours. He spends at most 12 hours on weight training. He spends at most 6 hours doing cardiovascular work. Let x denote the time (in hours) that Charlie spends doing cardiovascular work. Let y denote the time (in hours) that he spends on weight training. Shade the region corresponding to all values of x and y that satisfy these requirements.