Cut a circle into 16 parts on average and assemble it into an approximate rectangle with a circumference increased by 4 cm from the original one. Find the area of the original circle.
把一个圆平均剪16份，拼成一个近似的长方形，周长比原来增加了4厘米，求原来圆的面积．
<gadget id="calculator">4 / 2</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>