You can rain the offensive pressure down from different angles. This time White has a battery of two rooks but also a queen aimed at the key square from b4. The pressure against f8 is three against two (again the rook on f8 is irrelevant), so White just pounds away at the square until there is nothing left. He can start with his queen or one of his rooks; it doesn’t matter. The sequence might run 1. RxR+, RxR; 2. RxR+, QxR; 3. QxQ#.