There is a rectangle with a length of 9 cm and a width of 6 cm, what is its perimeter in cm?
有一个长方形，长9厘米，宽6厘米，它的周长是多少厘米？
<gadget id="calculator">9 + 6</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>