Watch, listen (with headphones), and take notes (on loose leaf paper) on the 6 of the videos on this page. Choose 2 videos on graphing, 2 videos on substitution, and 2 videos on elimination. Each video contains 1 example problem, therefor you should have 6 problems to turn in to the substitute once you have watched each video.
If you finish before the end of class, play one of these games. When asked to select a level, select hard: