①*4,得4x+4y+4z=204 ④①*4.5,得4.5x+4.5y+4.5z=229.5 ⑤②-④,得4y+z=96 z=96-4y ⑥③-⑤,得4.5y+3z=130.5 ⑦⑥代入⑦,得4.5y+288-12y=130.5 7.5y=157.5 y=21代入⑥,得z=96-84=12代入①,得x=51-21-12=18所以x=18,y...