2(3x-y)^2-4(3x-y)+5(5x-y)^2-6(3x-y)
=[2(3x-y)^2+5(5x-y)^2]+[-4(3x-y)-6(3x-y)]
=7(3x-y)^2-10(3x-y)
=(3x-y)[7(3x-y)-10]
=(3x-y)(21x-7y-10)