Use the Gauss–Jordan elimination

1) reverse rows 1 and 3;

2) add row 1 to row 3, multiply row 1 by –2 and add row 4;

3) multiply row 2: by 4 and add to row 3, by –1 and add row 3 to row 1;

4) devide row 3 by 14 and row 4 by –2;

5) subtract row 3 from row 4;

6) multiply row 3 by –3 and add to row 2;

7) multiply row 2 by 2 and add to row 1

So, and .