<PRE><B>Question 676152</B>
Hint:


3y-z=3


z = 3y - 3


------------------


x+2y+z=9 


x+2y+3y-3=9 


x+5y = 12


-----------------


5x-3y+7z=25


5x-3y+7(3y-3)=25


5x-3y+21y-21=25


5x+18y=46


So we then get the system


x+5y = 12
5x+18y=46


Solve this for x and y. Then use y to find z.</PRE>