An iron wire just encloses a square with a side length of 4 cm. If this iron wire is used to enclose a rectangle (with a side length of whole centimeters), what is the maximum area?
一根铁丝正好围成边长为4厘米的正方形，如果用这根铁丝围成长方形(边长是整厘米数)，它的面积最大有多大？
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<result>15</result>