2x-{-3y+[3x-2(3x-y)]}
=2x+3y-[3x-2(3x-y)]
=2x+3y-3x+6x+2y
=5x+5y
当x=-1,y=-1/5时
5x+5y=5*(-1)+5*(-1/5)=-5-1=-6