A parallelogram, the lengths of two adjacent sides are 20 cm and 15 cm respectively, find its perimeter.
一个平行四边形，相邻的两边长分别是20厘米和15厘米，求它的周长．
<gadget id="calculator">20 + 15</gadget>
<output>35</output>

<gadget id="calculator">35 * 2</gadget>
<output>70</output>

<result>70</result>