2(3x-y)²-4(3x-y)+5(3x-y)²-6(3x-y)
=27(3x-y)²-10(3x-y)
=27*(3*5/12+1/4)²-10*(3*5/12+1/4)
=27*(3/2)²-10*3/2
=243/4-15
=183/4