A rope with a length of 31.4 meters can go around this big tree exactly 10 times. What is the cross-sectional area of this big tree?
用一根长31.4米的绳子，正好能绕这棵大树10圈，这棵大树横截面的面积是多少？
<gadget id="calculator">31.4 / 10 / 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>