frog has to climb out of the mouth of a well 10 meters high. It climbs up 2 meters during the day and slides down 1 meter at night. How many days will it take for the frog to climb out of the wellhead?
一只青蛙要爬出10米高的井口．它每天白天向上爬2米，夜晚向下滑1米，多少天后青蛙才能爬出井口．
<gadget id="calculator">10 - 2</gadget>
<output>8</output>

<gadget id="calculator">2 - 1</gadget>
<output>1</output>

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

<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<result>9</result>