first eliminate a single variable from all equations
wait, if we divide the last equation by 2, we can eliminate x and y in first equation
divide last equation by 2
then times -1 to get
-x-y=-2
add to first equation to get
-z=-1
z=1
sub back
x+y-1=1
x+2(1)=0
x+y=2
now we gots
x+y=2
x=-2
solve
-2+y=2
y=4
x=-2
y=4
z=1
