x+y+z=3 x-y=8 5y+4z=-6

x - y = 8
x = y + 8

x + y + z = 3
(y + 8) + y + z = 3
2y + z = 3 - 8
2y + z = - 5 pers 1

2y + z = - 5 |×5
5y + 4z = - 6 |×2
10y + 5z = - 25
10y + 8z = - 12
-----------------------(-)
- 3z = - 13
z = 13/3

2y + z = - 5
2y + 13/3 = - 5
2y = - 5 - 13/3
2y = - 28/3
y = - 28/6

x = y + 8
x = - 28/6 + 48/6
x = 20/6