A cow is tied to a field of grass. If the rope to tie the cow is 7 meters long, how many square meters of grass can the cow eat at most?
在一片草地上拴着一头牛，如果拴牛的绳子长7米，这头牛最多可以吃到多少平方米的草？
<gadget id="calculator">7 ** 2</gadget>
<output>49</output>

<gadget id="calculator">3.14 * 49</gadget>
<output>153.86</output>

<result>153.86</result>