x+y+z+0.t=-1
x+0.y+z+t=5
x+0.y+z+t=7
x+y+0.z+t=4


1 1 1 0.1 | -1
1 0.1 1 1 | 5
1 0.1 1 1 | 7
1 1 0.1 1 | 4

1 1 1 0 | -1
1 0 1 1 | 5
1 0 1 1 | 7
1 1 0 1 | 4