Answer:
3
Explanation:
If you multiply the first equation by 2 and add the second, you eliminate z from the resulting equation.
If you add the first and third equations, you also eliminate z from the result.
Both of these resulting equations will have 3y as their second term, so you can subtract the first result from the second to eliminate the y variable and find the value of x.
This process has a shortcut. If we call the equations A, B, and C, the first elimination is done by calculating 2A+B. The second elimination calculates A+C. To find x, we compute ...
... (A+C) -(2A+B) = -A -B +C
... -(2x +y -z) -(-x +y +2z) +(3x +2y +z) = -3 -0 +9
... x(-2+1+3) +y(-1-1+2) +z(1-2+1) = 6
... 2x = 6
... x = 3
_____
Since this is a college math question, we presume you have a graphing calculator and are expected to know how to use it. The solution to systems of linear equations on such a calculator is usually pretty simple. A TI-84 can tell you the values of x, y, and z pretty easily: (x, y, z) = (3, -1, 2).