There is a stake on the grass, and a cow is tied to the stake. If the length of the rope to tie the cow is 3 meters, how many square meters of grass can the cow eat at most?
草地上有一个木桩，把一头牛栓在木桩上，若拴牛绳长3米，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>