The first one turns 9 upside down and turns 84 into 48, which means 6 times 8=48. Second, turn 9 into 6, and change 42 into 24, that is, 4 times 6=24. Third, turn a 6 into 9, and the exchange position is 54, which is 6 times 9=54. Fourth, turn 9 into 6, and the exchange position of 24 is 42, that is, 6 times 7=42.