A cow is tied to a wooden post. The length of the rope from the wooden post to the nose of the cow is 4 meters. How many square meters is the grass that the cow can eat?
一头牛栓在木柱上，木柱到牛鼻的绳长4米，牛可吃到草地的面积是多少平方米？
<gadget id="calculator">4 ** 2</gadget>
<output>16</output>

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

<result>50.24</result>