add the following;x-3y+4z,y-2x-8z and 5x-2y-3z

(x-3y+4z) + (y-2x-8z) + (5x-2y-3z)
= x-3y+4z +y-2x-8z +5x-2y-3z
= (x-2x+5x) + ( y-3y-2y) + (4z-8z-3z)
= 4x + (-4y) + (-7z)
= 4x - 4y - 7z