{2x+3y=m (1)
3x+2y=m+2 (2)
x+y=12 (3)
(2)-(1)得 x-y=2 (4)
(3)+(4)得 2x=14
x=7
x=7代入（3）得y=5
x=7,y=5代入（1）得
m=29