Gaussian Elimination: Need explanationto understanding this process anda solution on step by step.

1) x = -1

y + z = -5

x + 2x = -7

2) x - 4y = -8

y = 2

x + y +z = 5

3) 3x + y + 2z = 31

x + y + 2z = 19

x + 3y + 2z = 25

4) 2x + y + z = 5

x- y + 2z = 4

x + y + z = 4