If the perimeter of a square garden is 80 meters, what is the area of the garden?
一个正方形花圃的周长是80米，花圃的面积是多少．
<gadget id="calculator">80 / 4</gadget>
<output>20</output>

<gadget id="calculator">20 * 20</gadget>
<output>400</output>

<result>400</result>