here we got 2 equations, x+y+z=20, and 3x+2y+0.5z=20 then after solving last equation we get 6x+4y+z=40, from this one i do following: x+y+z+5x+3y=40, as x+y+z=20 then 20 +5x+3y=40, then 5x+3y=20,...