Решите систему уравнений x+3y=18 2x-3y-18

2х-3y=18 : 2x-3y=3
2х=18+3у
x=18+3y/2
2.
2(18+3y/2)-3y=3
4*18+3y-6y/2=6/2
4*18+3y-6y=6
72-3y=6
3y=6-72
3y=-66
y=-66|3
y=-22

2х-3y=18
2x-3(-22)=18
2x+66=18
2x=18-66
2x=48
x=24