x=4+yz=y+5x-z=(4+y)-(y+5)=4+y-y-5=-1
y-z=-5y=z+5x-y=4x-(z+5)=4x-z-5=4x-z=9
X-Y+Y-Z=Y-Z=4+5=9
x-z=x-y+y-z=4-5=-1