Solve: x+y+z=6, 2x-y+z=3, 3x-z=0}

from 3: 
z=3x 
1 plus 2: 
(2x-y+z)+(x+y+z)=3+6 
3x+2z=9 
3x+2(3x)=9 
9x=9 
x=1 
so z=3 
from 1: 
x+y+z=1+y+3=6 
y+4=6 
y=2 

Solution: (1,2,3) 


:)