After a 10-meter-long rope is wrapped around a tree trunk 3 times, the remaining length is 0.58 meters. What is the cross-sectional area of the tree trunk?
一根长10米的绳子绕一棵树干3圈后，余0.58米．这棵树干的横截面积是多少平方米？
<gadget id="calculator">10 - 0.58</gadget>
<output>9.42</output>

<gadget id="calculator">9.42 / 3</gadget>
<output>3.14</output>

<gadget id="calculator">3.14 / 3.14 / 2</gadget>
<output>0.5</output>

<gadget id="calculator">0.5 ** 2</gadget>
<output>0.25</output>

<gadget id="calculator">3.14 * 0.25</gadget>
<output>0.785</output>

<result>0.785</result>