An automatic rotary irrigation device, its sprinkling surface is a circle with a radius of 4 meters, what is the sprinkling area of this device in square meters?
一种自动旋转灌溉装置，它的喷灌面是一个半径为4米的圆形，这种装置的喷灌面积是多少平方米．
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<result>50.24</result>