In the system {x+y+z=6x−y+2z=52x+y−z=4\begin{cases} x + y + z = 6 \\ x - y + 2z = 5 \\ 2x + y - z = 4 \end{cases}⎩⎨⎧x+y+z=6x−y+2z=52x+y−z=4, what is x−yx - yx−y?
111
57\dfrac{5}{7}75
222
−1-1−1