-x+2y=-9, 5x-2y= 21.. Berapa 2x-3y =...

4x=12
x=3
2y=3-9
y=-3
2x-3y=6+9=15

-x+2y=-9
5x-2y= 21
–––––––––(ditambah)
4x=12
x=3

-x+2y=-9
-3+2y=-9
2y=-6
y=-3

maka
2x-3y=
2(3)-3(-3)=
6+9=15

......................................