Y + -Y=0. 2X=34 Then divide both sides by the number next to "X." X=17 Then substitute X=17 into X+Y=21. Then you get 17 +Y=21. Y=21-17=4 Next check your answers by substituting into each equation above to see if both work and are true. 17+4=21
21=21
17-4=13
13=13
