Not factor theorem. Just basic finding the common factor. i.e. x^2y + xy^2, common factor is xy, so you get xy(x+y). Or 8x^2 + 6x, common factor is 2x, so 2x(4x+3).
These questions are the next step from that, because the common factor isn't just xy or 2x, but is in the form (a+b), which makes...