If the lengths of two adjacent sides of a parallelogram are 9 cm and 5 cm respectively, what is its perimeter?
平行四边形相邻两边长分别是9厘米和5厘米，它的周长是多少．
<gadget id="calculator">9 + 5</gadget>
<output>14</output>

<gadget id="calculator">14 * 2</gadget>
<output>28</output>

<result>28</result>