After cutting a circular piece of paper, assemble it into an approximate rectangle whose width is equal to the radius and whose area is constant. The perimeter of this rectangle is 16.56 cm. What is the area of this approximate rectangle?
把一个圆形纸片剪开后，拼成一个宽等于半径，面积不变的近似长方形，这个长方形的周长是16.56厘米，这个近似的长方形的面积是多少？
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>