posted by anonymous .
solve the system by elimination.
Multiply the last equation (both sides) by 2. That gives you
4x + 6y - 4z = 18
Add that to
6x - 6y - 4z = -10
That gives you
10x -8z = 8
So far, we have eliminated the variable y.
Use similar tricks to get rid of x or z.
I believe your second equation is typed incorrectly. Did you mean
-5x +4y -z = -12?