Question 253952
1)x+y-2z=0
2)3x+y=1
3)5x+3y+7z=2 

From equation 1 we have y=2z-x 

So if (from equation 2) 3x+y = 1 then

3x+(2z-x)= 1

3x+2z-x = 1 

and 

From equation 3:

5x+3*(2z-x) + 7z = 2

Solve these two equations for x an z then substitute in the first equation to find y.