Help solve this picture

X + y - z = 9
3x - y + z = -13
(+)___
4x =  -4 => x = -1 => y - z = 10;
But, x - 2y + 4z = -1 => -2y + 4z = 0 => -y + 2z = 0;

 y  -  z = 10
-y + 2z = 0
(+)__
/       z = 10 =>   y = 20 .

A. There is one solution. The solution is ( - 1, 20, 10 ).