Sorry, I was wrong. Day 1: It's not 3 meters during the day, but 2 meters at night, 1 meter. Eight meters left. The next day: no, 3 meters in the daytime, 5 meters left, 2 meters in the evening, and 7 meters left. Day 3: No, 3 meters during the day, 4 meters left, 2 meters at night, and 6 meters left. Day 4: There is no 3m in the daytime, 2m in the evening and 5m in the evening. Day 5: 2 meters left, 4 meters left. Day 6: 65438+ 0 meters left, 3 meters left. Day 7: There are 0 meters left, and 7 days are over. Attention! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! The first day is after smoking, and there is still 9-3=6 meters. Note that this is a day. This is 1 to be added. So, how many days does it take to drop from 6 meters to 0 meters? It takes x days to drop to 1 m every day. Then 6- 1x=0 x=6 1x goes down every day, and it takes several days for 6 to go down to 0, so 1+6=7 days. You see I'm right! I'm speechless ~ ~ ~ ~ I'm a senior one math expert! I can give reasons for my answer! Because I have enough strength!

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