Before climbing out of the well, the snail climbs 3-2= 1 meter every day. Assuming that the snail can climb out of the wellhead in n days, it climbed (n- 1) meters in the first n- 1 day, and climbed 3 meters in the last day (n-day), to climb out of the wellhead, there are:

(n- 1)+3 & gt； = 15, that is, n+2 >; = 15。 = 13。

Snail/kloc-can climb out of the wellhead in 0/3 days. Climbed 12 days ago 12 meters, climbed 3 meters during the day on 13 days, and just climbed out of the wellhead.