Uncle Wang wants to use a 31.4-meter-long fence to enclose a vegetable garden in the backyard. To make the area larger, should it be a square or a circle? What is the largest area of the surrounding vegetable garden?
王大伯想用31.4米长的栅栏在后院围一个菜园，要使面积大一些，该围成正方形好还是圆形好呢？围的菜园面积最大是多少？
<gadget id="calculator">31.4 / 3.14 / 2</gadget>
<output>5</output>

<gadget id="calculator">5 ** 2</gadget>
<output>25</output>

<gadget id="calculator">3.14 * 25</gadget>
<output>78.5</output>

<result>78.5</result>