x+y+z=5 ① 4x+8y+5z=300 ② x+y+2z=67 ③
③-①,z=62
代入①、②,x+y=-57 ④,4x+8y=-10 即x+2y=-2.5 ⑤
⑤-④,y=54.5
代入④,x=-111.5