-3(2x-y)-｛7x-〔6x+2x-(10x-8y)〕-x-2(3x-4y)｝
=-6x+3y-｛7x-〔8x-10x+8y)〕-x-6x+8y｝
=-6x+3y-｛7x-〔-2x+8y)〕-7x+8y｝
=-6x+3y-｛7x+2x-8y-7x+8y｝
=-6x+3y-｛2x｝
=-8x+3y