=9s(s-1)-12ts+2t(2t+3) =3s(3s-3-2t)+2t(-3s+2t+3) =(3s-2t-3)(3s-2t)
=9s(s-1)-12ts+2t(2t+3)=3s(3s-3-2t)+2t(-3s+2t+3)=(3s-2t-3)(3s-2t)