A piece of iron wire can just enclose a square with a side length of 4 decimeters. If this wire is used to enclose a rectangle, what is the maximum area of it?
一根铁丝正好能围成边长是4分米的正方形，如果用这根铁丝围成长方形，它的面积最大是多少平方分米？
<gadget id="calculator">4 * 4</gadget>
<output>16</output>

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">8 / 2</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">5 * 3</gadget>
<output>15</output>

<result>15</result>