请帮我解方程第九道 5x-4y+4z=13 2x+7y-3z=19 3x+2y-2=18

5x-4y+4z=13 →5x+4(y-z)=13 (1)
2x+7y-3z=19 (2)
3x+2y-2z=18 →3x+2(y-z)=18 (3)
→6x+4(y-z)=36 (4)
(4)-(1)得 x=23
7y-3z=-27 →14y-6z=-54
2y-2z=-51 →6y-6z=-153
y=99/8
z=303/8