7y(x-3y)^2-2(3y-x)^3
=7y(x-3y)^2+2(x-3y)^3
=(x-3y)^2 [7y+2(x-3y)]
=(x-3y)^2 (2x+y)
把2x+y=-6,x-3y=4,代入,
原式=(x-3y)^2 (2x+y)=16×(-6)= -96