Resposta :
Eu irei resolver por Kramer:
D=|1 1 1|=(4+20+9)-(6+12+10)=33-28=5
|3 2 4|
|5 3 2|
Dx=|0 1 1|=(0+16+21)-(14+0+8)=37-22=15
|7 2 4|
|4 3 2|
Dy=|1 0 1|=(14+0+12)-(0+16+35)=26-51=-25
|3 7 4|
|5 4 2|
x=Dx/D=15/5=3
y=Dy/D=-25/5=-5
x+y+z=0
3-5+z=0
z=2
x=3
y=-5
z=2