There is a stake in the grass, and a cow is tied to the stake with a 3-meter-long rope. How many square meters of grass can the cow eat at most?
草地上有一根木桩，用一根3米长的绳子将一头牛拴在木桩上，这头牛最多可以吃到多少平方米的草？
<gadget id="calculator">3 ** 2</gadget>
<output>9</output>

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

<result>28.26</result>