What is the lateral area of a cylinder surrounded by a square paper with a circumference of 20cm in cm**2.
用一张周长20cm的正方形纸围成一个圆柱围成的圆柱的侧面积是多少cm**2．
<gadget id="calculator">20 / 4</gadget>
<output>5</output>

<gadget id="calculator">5 * 5</gadget>
<output>25</output>

<result>25</result>