Again, start by looking for the ingredients of a double attack. Black has a loose rook at a8: a good target if you can take advantage of it. So ask whether you can check his king and attack the rook at the same time. Well, you can't; but are there any squares from which it could be done, whether or not they now are within reach? Yes: in principle c6 would work, though at present it's protected and the queen's path to it is blocked. Look to see what stands in the way; ask what methods you have for clearing the queen’s path through—and especially what exchanges. The natural answer is 1. RxN, d7xR, 2. Qxc6+, recapturing the rook and winning a piece and a pawn. Notice how the single blow (RxN) takes care of both of White's problems at once, getting his own rook out of the way and forcing Black to replace the protected occupant of c6 with a loose pawn.