The diameter of a radar circular screen is 80 cm, find the area of the screen.
一个雷达圆形屏幕的直径80厘米，求屏幕的面积．
<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">40 ** 2</gadget>
<output>1_600</output>

<gadget id="calculator">3.14 * 1_600</gadget>
<output>5_024</output>

<result>5_024</result>