If a circular piece of paper is cut into two equal semicircles, the circumference is increased by 40cm, what is the area of the original circle?
将一个圆形纸片剪成两个相等的半圆，周长增加了40cm，原来圆的面积是多少．
<gadget id="calculator">40 / 2 / 2</gadget>
<output>10</output>

<gadget id="calculator">10 ** 2</gadget>
<output>100</output>

<gadget id="calculator">3.14 * 100</gadget>
<output>314</output>

<result>314</result>