Use elimination with the bottom two equations to get 8x + 7z = 1
Multiply the first equation by 2 and then do the same thing with the first two equations.
4x + 6z = 18
Now with these two new equations that only have two variables, do elimination again after multiplying 4x + 6z = 18 by -2 so that the x terms cancel out.
-5z = -35
z = 7
Now plug 7 in for z in one of the new equations to find x.
4x + 6(7) = 18
4x = -24
x = -6
Now use one of the original equations and plug 7 and -6 in to find y.
-6 + y + 7 = 3
y = 2
