(4x-2y-z)-{5x-[8y-2z-(x+y)]-2(3y-10z)}
=4x-2y-z)-{5x-[8y-2z-X-Y)]-6Y+20Z
=4x-2y-z-5x+8y-2z-X-Y-6Y+20Z
=-2X-Y+17Z