x - y + z = -7
x + y + z = 1
-------------------add
2x + 2z = -6
x + y + z = 1
x + y - z = 9....multiply by -1
-------------------
x + y + z = 1
-x - y + z = -9 (result of multiplying by -1)
------------------add
2z = -8
z = -8/2
z = -4
2x + 2z = -6
2x + 2(-4) = -6
2x - 8 = -6
2x = -6 + 8
2x = 2
x = 1
x - y + z = -7
1 - y - 4 = -7
-y -3 = -7
-y = -7 + 3
-y = -4
y = 4
so x = 1, y = 4, and z = -4
