The length of a rectangle is 9 cm, the width is 4 cm, what is the circumference in cm?
长方形长9厘米，宽4厘米，周长多少厘米．
<gadget id="calculator">9 + 4</gadget>
<output>13</output>

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

<result>26</result>