In a rectangle with a width of 4 cm and a length of 4.2 cm, cut a circle as large as possible. What is the area of this circle?
在一个宽4厘米，长4.2厘米的长方形中，割一个尽可能大的圆，这个圆的面积为多少．
<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>