Uncle Wang wants to use 31.4 meters of wire to enclose a vegetable garden in his backyard. To make the area as large as possible, what shape should be encircled? What is the area?
王大爷想用31.4米的铁丝在自家的后院围一个菜园，要使面积尽量的大，该围什么图形呢？面积是多少？
<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>