Someone measured that the circumference of a trunk is 15.7 centimeters, what is the area of the cross section of the trunk in square centimeters?
有人测得一棵树干的周长是15.7厘米，这棵树干的横截面的面积是多少平方厘米．
<gadget id="calculator">15.7 / 3.14 / 2</gadget>
<output>2.5</output>

<gadget id="calculator">2.5 ** 2</gadget>
<output>6.25</output>

<gadget id="calculator">3.14 * 6.25</gadget>
<output>19.625</output>

<result>19.625</result>