If the sum of the two adjacent sides of a rectangle is 20 cm, what is the perimeter of the rectangle in cm?
一个长方形相邻的两条边的长度和为20厘米，这个长方形的周长是多少厘米．
<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>