Question

Is my answer correct, if now can you explain​

Answer 1

Yes. The first step is to set up the equations so that one unknown cancels out: here, the z's will cancel out:

5z+4y=-14

3z+6y=-6

-15z-12y=42

15z+30y=-30

8y=12

y=1.5

3z+6y=-6

3z+6(1.5)=-5-9

z=-14/3