The two adjacent sides of a parallelogram are 3cm and 7cm respectively. What is the perimeter of this parallelogram?
平行四边形的相邻两条边分别为3cm、7cm，这个平行四边形的周长是多少．
<gadget id="calculator">3 + 7</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<result>20</result>