x+y=5 y+z=6 2x+2y+z=4 cara mesubtisusikan

2x + 2y + z = 4
x + y = 5

2x + 2y + z = 4
2x + 2y = 10
––––––––––– –
z = -6

y + z = 6
y + (-6) = 6
y = 12

x + y = 5
x + 12 = 5
x = -7