A rope is wrapped around a big tree. If it is wrapped 10 times, there will be 3 meters left. If it is wrapped 12 times and there is a gap of 3 meters, then how many meters will be left after 8 times.
一根绳子，围着大树，如果绕10圈则剩3米，如果绕12圈又缺3米，那么绕8圈剩多少米．
<gadget id="calculator">3 + 3</gadget>
<output>6</output>

<gadget id="calculator">12 - 10</gadget>
<output>2</output>

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

<gadget id="calculator">3 * 10</gadget>
<output>30</output>

<gadget id="calculator">8 * 3</gadget>
<output>24</output>

<gadget id="calculator">3 - 24</gadget>
<output>-21</output>

<gadget id="calculator">30 + (-21)</gadget>
<output>9</output>

<result>9</result>