There is a circular flower bed in the central square with a diameter of 8m. To build a path around it, the perimeter of the path is 31.4m. What is the area of the trail?
中心广场有一个圆形花坛，直径是8m．要在它的周围修一条小路，小路周长是31.4m．小路面积是多少？
<gadget id="calculator">31.4 / 3.14 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

<gadget id="calculator">25 - 16</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>