Ok, I think I understand:
-3x+2y=1
+3x +3x
2y=3x+1
/2 /2 /2
y=3/2x+1/2
-7x+9(3/2x+1/2)=-2
-7x+27/2x+9/2=-2
-7x+27/2x+9/2=-2
-9/2 -9/2
-7x+27/2x=-2/1-9/2
-7x+27/2x=-4/2-9/2
-7x+27/2x=-13/2
13/2x=-13/2
13/2 13/2
x=-1
-3(-1)+2y=1
3+2y=1
-3 -3
2y=-2
2 2
y=-1