If a rectangle or a square is surrounded by 16 cm long iron wire, what is the maximum area of the enclosed figure in square centimeters?
用长16厘米的铁丝围成长方形或者正方形，围出的图形面积最大是多少平方厘米．
<gadget id="calculator">16 / 4</gadget>
<output>4</output>

<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<result>16</result>