- Period 1: http://www.quia.com/pages/elopez518/page6
- Period 3: http://www.quia.com/pages/elopez518/page7
- Period 5: http://www.quia.com/pages/elopez518/page8
- Period 4: http://www.quia.com/pages/elopez518/page3
- Period 6: http://www.quia.com/pages/elopez518/page5