A wire can enclose a circle with a diameter of 40 cm. Now it encloses a square. What is the side length of this square in cm?
一根铁丝可以围成一个直径是40cm的圆，现在把它围成一个正方形，这个正方形的边长是多少cm．
<gadget id="calculator">40 / 4</gadget>
<output>10</output>

<gadget id="calculator">3.14 * 10</gadget>
<output>31.4</output>

<result>31.4</result>