A cow is tied to the grass, and the length of the rope to tie the cow is 6m. What is the maximum area that the cow can graze?
草地上拴有一头牛，拴牛的绳子长6m，这头牛最多可以吃草的面积是多少？
<gadget id="calculator">6 ** 2</gadget>
<output>36</output>

<gadget id="calculator">3.14 * 36</gadget>
<output>113.04</output>

<result>113.04</result>