因为x-2y=m-4 => x=m-4+2y
代入3x+2y=3m => 3m-12+6y+2y=3m => 8y=12 => y=1.5
这时可以把x-2y=m-4加上3x+2y=3m,=> 4x=4m-4 => x=m-1
然后把x=m-1和y=1.5代入x+4y=2m+3,
m-1+6=2m+3 => m=2