If a rope is wrapped 10 times around a big tree, there will be 4 meters left, and if it is wrapped 11 times around the big tree, there will be a difference of 1 meter. If the rope is wrapped 8 times around the tree, how many meters will there be left?
一根绳子如果绕一棵大树10圈，则剩4米，如果绕这棵大树11圈，则又差1米．这跟绳子如果绕这棵大树8圈，则剩多少米．
<gadget id="calculator">10 * 2.5</gadget>
<output>25</output>

<gadget id="calculator">25 + 4</gadget>
<output>29</output>

<gadget id="calculator">8 * 2.5</gadget>
<output>20</output>

<gadget id="calculator">29 - 20</gadget>
<output>9</output>

<result>9</result>