If a rectangle with a length of 20 cm and a width of 5 cm is transformed into a square of equal area, find the perimeter of the square.
把一个长为20厘米，宽为5厘米的长方形变为等面积的正方形，求正方形的周长．
<gadget id="calculator">10 * 4</gadget>
<output>40</output>

<result>40</result>