A 15m long rope is wrapped around a tree trunk 5 times, and there is still 2.44m left. What is the approximate radius of this tree trunk?
一条长15m的绳子围绕一棵树干，绕了5圈，还余下2.44m．这棵树干的半径大约是多少米？
<gadget id="calculator">15 - 2.44</gadget>
<output>12.56</output>

<gadget id="calculator">12.56 / 5 / 3.14 / 2</gadget>
<output>0.4</output>

<result>0.4</result>