Multiple both sides of the second equation by 2: 12x-2y+6z=24. Add this equation to the third equation 8x+2y+4z=6: 20x+10z=30, or 2x+z=3. Check all the answers, only B satisfies this (x=1, z=1). Therefore, the answer must be b. You can also check that y=-3 satisfies other equations too.
