A dry well, there is a snail at the bottom of the well, the snail climbs up 3 meters along the wall of the well during the day, and slides down 2 meters at night, when the snail just climbs to the mouth of the well in the afternoon of the tenth day, what is the depth of the well ?
一口枯井，井底部有一只蜗牛，这只蜗牛白天沿着井壁向上爬3米，夜间又滑下2米，到了第十天下午这只蜗牛恰好爬到井口，则这口井的深度是多少？
<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">1 * 9</gadget>
<output>9</output>

<gadget id="calculator">9 + 3</gadget>
<output>12</output>

<result>12</result>