What is the perimeter of a rectangle whose length is 8 cm and width is 5 cm?
一个长方形的长8厘米，宽是5厘米，它的周长是多少．
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<result>26</result>