Find the area of each circle below. R=4 cm D=5 cm C=62.8 meters.
求下面各圆的面积．R=4厘米D=5厘米C=62.8米．
<gadget id="calculator">62.8 / 3.14 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<result>314</result>