Two snails fled from the top of the well to the bottom because they couldn't stand the sunlight. Climbing down during the day, the two snails crawl at different speeds during the day, one climbs 20 decimeters during the day, and the other climbs 15 decimeters. Sliding down in the dark, the two snails slide at the same speed. As a result, one snail took exactly 5 days and nights to reach the bottom of the well, and the other snail took exactly 6 days and nights to reach the bottom of the well. So, how deep is the well?
两只蜗牛由于耐不住阳光的照射，从井顶逃向井底．白天往下爬，两只蜗牛白天爬行的速度是不同的，一只每个白天爬20分米，另一只爬15分米．黑夜里往下滑，两只蜗牛滑行的速度却是相同的．结果一只蜗牛恰好用5个昼夜到达井底，另一只蜗牛恰好用6个昼夜到达井底．那么，井深多少米？
<gadget id="calculator">30 * 5</gadget>
<output>150</output>

<gadget id="calculator">150 / 10</gadget>
<output>15</output>

<result>15</result>