Looking at the attached image, we start with 3 red circles (representing 3) and 2 green ones (representing 2p) on one side and 7 red circles (representing 7) on the other side. We then cross out 3 red circles from each, and since 2 green circles are left, we split the remainder of each side into half represented by grey lines (as 1*2=2). Crossing out half from each side, we end up with one green circle (p)=2
