12x12=144+144-88=200 good luck!
In augmented matrix form, the system is equivalent to
Subtract row 1 from row 2, and 4(row 1) from row 3:
Divide through row 2 by -2, and through row 3 by -3:
Subtract row 2 from row 3:
Divide through row 3 by 2:
The last row tells you . Then
and