12qr+6r-18rs=
8m+4m-2mn=
8b+2bc-4bd=
12zr+6z-4=
8t+16tu-24tv=
2m(4+2-n)
6r(2q+1-35)
8t(1+2u-3v)
2(6zr+3z-2)
2b(4+c-2d)
