Two rectangles with a length of 8 cm and a width of 4 cm are used to form a large rectangle. What is the perimeter of the large rectangle in cm?
用两个长8厘米、宽4厘米的长方形拼成一个大的长方形，这个大长方形的周长是多少厘米．
<gadget id="calculator">8 + 8 + 4</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>