Chapter 9 - Section 9.1 - Solving Systems of Linear Equations in Three Variables and Problem Solving - Exercise Set - Page 637: 15

$x=6, y =22, z=-20$

We add the first and second equation to get $$3x=18$$ or $$x=6$$ We then multiply the 1st equation by 3 to get, $3x+3y+3z=24$ We add that to the last equation to get, $$4x+y=46$$ or $$24+y=46$$ $y=22$ Plugging x and y into the first equation gives us, $z=-20$