A rope for tying a cow is 8 meters long, how big is the area where the cow can eat grass?
一根拴牛的绳子长8米，牛能吃到草的面积有多大？
<gadget id="calculator">8 ** 2</gadget>
<output>64</output>

<gadget id="calculator">3.14 * 64</gadget>
<output>200.96</output>

<result>200.96</result>