You have to put the problems on top of each other. Then choose whether you want to isolate x or y. (I would say try it with x that is easier) If you multiply the (15x+3y=9) all by -2. Then you write the answers there. Then place 10x+7y=-4 underneath leaving that the same. Cross out the x currently and solve for y as you would normally. Plug in the y once you figure it out and then solve for x. Then check your answer.
