The length of a rectangle is 9 cm and the width is 6 cm. What is its perimeter?
长方形的长是9厘米，宽是6厘米，它的周长是多少．
<gadget id="calculator">9 + 6</gadget>
<output>15</output>

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

<result>30</result>