If a rope is wrapped 9 times around a big tree and there is 4 meters left, if it is wrapped 10 times around a big tree and there is 1 meter missing, then how many meters are left after 8 times.
一根绳子围着大树绕9圈剩4米，如果围着大树绕10圈又缺1米，那么绕8圈还剩多少米．
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">10 - 9</gadget>
<output>1</output>

<gadget id="calculator">5 / 1</gadget>
<output>5</output>

<gadget id="calculator">9 * 5</gadget>
<output>45</output>

<gadget id="calculator">45 + 4</gadget>
<output>49</output>

<gadget id="calculator">5 * 8</gadget>
<output>40</output>

<gadget id="calculator">49 - 40</gadget>
<output>9</output>

<result>9</result>