Problem 1:

x + 2y - z = -2

x + z = 0

2x - y - z = -3

Problem 2:

2x - 3y - z = 13

-x + 2y - 5z = 6

5x - y - z = 49

The answer to problem 3 (that I got) is: x = -1, y = 0, z = 1

Is this correct?

For problem 4, do I use Gaussian elimination or Gauss-Jordan elimination?

Thanks in advance!