x+y+z=18两边乘3得3x+3y+3z=54
8x+6y+6z=118两边同除2得4x+3y+3z=59
两式相减得x=5,代入x+y+z=18得y+z=13,与2y+z=20 作差得y=7
故z=6
所以x=5,y=7,z=6