What is the largest area in square meters of a rectangle with a perimeter of 20 meters?
周长为20米的矩形的面积最大是多少平方米．
<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

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

<result>25</result>