Solve the system using matrix methods or substitution: {x−2y+z=42x+y−z=1x+y+z=3\begin{cases} x - 2y + z = 4 \\ 2x + y - z = 1 \\ x + y + z = 3 \end{cases}⎩⎨⎧x−2y+z=42x+y−z=1x+y+z=3 What is x+y+zx + y + zx+y+z?
333
−3-3−3
000
666