The problem: "one week trey rented 4 dvds and 2 video games for $18. the next week he rented 2 dvds and 1 video game for $9. find the rental costs for each video game and dvd. explain your answer." i know the equations (4x+2y=18, and 2x+1y=9) and the answer, but i'm really confused as to what work i should show as my teacher requires it, substitution and elimination don't work, so i don't know what to do. .