2z+5y=63|*7
z+7y=5|*-5
14z+35y=441
-5z-35y=-25
14z+35y+(-5z)-35y=441+(-25)
9z=416
z=416/9
416/9+7y=5
7y=5-416/9
7y=-371/9
y=-371/9:7
y=-53/9
2z+5y=63|*7
z+7y=5|*-5
14z+35y=441
-5z-35y=-25
14z+35y+(-5z)-35y=441+(-25)
9z=416
z=416/9
416/9+7y=5
7y=5-416/9
7y=-371/9
y=-371/9:7
y=-53/9