A snail wanted to climb out of the dry well to see how big the sky was. It climbs up 3 meters during the day and retreats 2 meters at night. It was not until the eighth day that I climbed to the mouth of the well. How many meters deep is this dry well? ?
一只蜗牛想从枯井里爬出来看看天有多大．它每天白天爬上3米，晚上又退下去2米．整整爬到第8天才爬到井口．这口枯井有多少米深．？
<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<gadget id="calculator">1 * 7</gadget>
<output>7</output>

<gadget id="calculator">7 + 3</gadget>
<output>10</output>

<result>10</result>