3x + 2y - z = 18 X + 4y + z = 20 -2x + y -z = 3

3x+2y-z=18
x+4y+z=20
----------------- +
4x+6y =38

x+4y+z=20
-2x+y-z=3
----------------- +
-x+5y =23

4x+6y=38 × 1
-x+5y=23 ×4

4x+6y=38
-4x+20y=92
------------------- +
26y=130
y=5

4x+6y=38
4x+6.5=38
4x+30=38
4x=38-30
4x=8
x=2

3x+2y-z=18
3.2+2.5-z=18
6 + 10 -z =18
-z=18-16
-z=2
z =-2

jadi x=2 ,y=5 ,z= -2