x+2y+3z=15 (1)
(x+4y)/3=3
x+4y=9 (2)
(y-3z)/4=3
y-3z=12 (3)
(1)+()
x+3y=27 (4)
(2)-(4)
y=-18
x=27-3y=81
z=(y-12)/3=-10