Uncle Li discovered an ancient tree during an expedition, and measured the circumference of the circular trunk to be 21.98 meters. What is the area of the cross-section of the tree?
李叔叔在一次探险活动中，发现了一棵古老的树，测出圆形树干的周长是21.98米．这棵树横截面的面积是多少？
<gadget id="calculator">21.98 / 3.14 / 2</gadget>
<output>3.5</output>

<gadget id="calculator">3.5 ** 2</gadget>
<output>12.25</output>

<gadget id="calculator">3.14 * 12.25</gadget>
<output>38.465</output>

<result>38.465</result>