The lengths of two adjacent sides of a parallelogram are 3 cm and 7 cm respectively. What is the perimeter of this parallelogram?
平行四边形相邻两边的长分别是3厘米，7厘米，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>