Convert a circle into a rectangle. The perimeter of the rectangle is 16.56 cm. What is the area of the circle in square centimeters?
把一个圆转化成长方形，长方形的周长是16.56厘米，圆的面积是多少平方厘米．
<gadget id="calculator">3.14 * 2</gadget>
<output>6.28</output>

<gadget id="calculator">6.28 + 2</gadget>
<output>8.28</output>

<gadget id="calculator">16.56 / 8.28</gadget>
<output>2</output>

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

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

<result>12.56</result>