A square vegetable field has a circumference of 40 meters, what is the area in square meters?
一块正方形菜地，周长40米，它的占地面积是多少平方米．
<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">10 * 10</gadget>
<output>100</output>

<result>100</result>