Chapter 9 - Section 9.1 - Solving Systems of Linear Equations in Three Variables and Problem Solving - Exercise Set - Page 639: 37

18, 13, 9

$x+y+z=40$ $x=y+5$ $x=2*z$ $x=y+5$ $x-5=y+5-5$ $x-5=y$ $x=2z$ $x/2=2z/2$ $x/2=z$ $x+y+z=40$ $x+(x-5)+(x/2)=40$ $x+x-5+x/2=40$ $2.5x-5=40$ $2.5x-5+5=40+5$ $2.5x=45$ $2.5x*2=45*2$ $5x=90$ $5x/5=90/5$ $x=18$ $x=2z$ $18=2*z$ $18/2=2*z/2$ $9=z$ $x+y+z=40$ $18+y+9=40$ $27+y=40$ $27+y-27=40-27$ $y=13$