White’s knight is on a dark square, as are Black’s king, queen, and both rooks; a fork at g6 suggests itself. The square is protected—how many times? Twice: by the queen and by the pawn at h7. The pawn is pinned by White’s queen, so the problem is just the defense of g6 by Black’s queen. Consider whether it is protecting any pieces that you might take and you see that it guards the rook at f8 and bishop at e5. You can’t capture the bishop, but you can take the rook with RxR. This looks a lot like the previous problem, but with a small difference: the rook at f8 is protected twice—by the other rook at d8 as well as by the queen. If Black retakes with his other rook instead of with his queen, you still won’t have a fork. But then you will have another rook at f1 that you can use to attack again. Hence: 1. RxR+, RxR; 2. RxR+, QxR; 3. Nxg6+ and the fork is complete. Think of this just as a case where two exchanges were needed to lure away the guardian rather than one.