A calf is tied to a tree with a rope 3 meters long. What is the approximate area of grass that this calf can eat?
在一棵树上用3米长的绳子拴着一头小牛．这只小牛可以吃到的草的面积约是多少？
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

<gadget id="calculator">3.14 * 9</gadget>
<output>28.26</output>

<result>28.26</result>