9. A rope of 42 meters is wound around the trunk of a big tree exactly 10 times. What is the diameter of the trunk of the big tree in centimeters?
9.42米绳子刚好在一根大树树干上绕了10圈，大树树干的直径是多少厘米．
<gadget id="calculator">9.42 / 10 / 3.14</gadget>
<output>0.3</output>

<gadget id="calculator">0.3 * 100</gadget>
<output>30</output>

<result>30</result>