Xiao Ming tied a cow to a stake in the grass. The rope is 3 meters long. What is the maximum area of grass that the cow can eat?
小明把一头牛拴在草地的木桩上，绳子长3米，这头牛能吃到的草的面积最大是多少？
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<result>28.26</result>