A circle with a diameter of 20 cm can be enclosed by a piece of iron wire. If it is surrounded by a square, what is the side length of the square?
用一根铁丝可以围成直径为20厘米的圆，如果将它围成正方形，那么正方形的边长是多少厘米？
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">3.14 * 5</gadget>
<output>15.7</output>

<result>15.7</result>