3x*2-10xy+3y*2+9x+5y-12
=(3x-y)(x-3y)+12x-4y-3x+9y-12
=(3x-y)(x-3y)+4(3x-y)-3x+9y-12
=(3x-y)(x-3y+4)-3(x-3y+4)
=(x-3y+4)(3x-y-3)