Chapter 9 - Section 9.1 - Solving Systems of Linear Equations in Three Variables and Problem Solving - Exercise Set - Page 640: 41

$x=60$ degrees, $y=55$ degrees, $z=65$ degrees

$2x+5+y=180$ $2x-5+z=180$ $x+y+z=180$ $2x+y+5=180$ $2x+y=175$ $2x+z-5=180$ $2x+z=185$ $2x+y+2x+z=175+185$ $4x+y+z=360$ $x+y+z=180$ $4x+y+z-x-y-z=360-180$ $3x=180$ $3x/3=180/3$ $x=60$ $2x+y=175$ $2*60+y=175$ $120+y=175$ $y=55$ $2x+z=185$ $2*60+z=185$ $120 + z=185$ $z=65$