由①得,3x-15=3y-6,即：x-y=3……③
由②得,2(x-y)-(x+2y)=12,即：x-4y=12……②
③-②得,3y=-9,y=-3
把y=-3代入③得,x+3=3,∴x=0
∴{x=0 y=-3