Chapter 9 - Section 9.1 - Solving Systems of Linear Equations in Three Variables and Problem Solving - Exercise Set - Page 638: 20

$(2, 1, 1)$

A: $4x+y-z=8$ B: $x-y+2z=3$ C: $3x-y+z=6$ A+C $4x+y-z+3x-y+z=8+6$ $7x=14$ $7x/7=14/7$ $x=2$ B-2C $x-y+2z-2*(3x-y+z)=3-2*6$ $x-y+2z-6x+2y-2z=3-12$ $-5x+y=-9$ $-5*2+y=-9$ $-10+y=-9$ $y=1$ $4x+y-z=8$ $4*2+1-z=8$ $8+1-z=8$ $1-z=0$ $z=1$