A snail fell into a well 10 meters deep. It climbed up 4 meters every day during the day and slid down 2 meters at night. How many days did it reach the mouth of the well?
一只蜗牛掉进一口10米深的井里，它每天白天爬上4米，夜里下滑2米，第多少天到达井口．
<gadget id="calculator">10 - 4</gadget>
<output>6</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">6 / 2</gadget>
<output>3</output>

<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>