The diameter of a circular manhole cover is 8 decimeters, what is its area in square decimeters?
一个圆形井盖的直径是8分米，它的面积是多少平方分米．
<gadget id="calculator">8 / 2</gadget>
<output>4</output>

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

<gadget id="calculator">3.14 * 16</gadget>
<output>50.24</output>

<result>50.24</result>