rectangle has a length of 7 cm and a width of 3 cm, what is its perimeter in cm?
一个长方形的长是7厘米，宽是3厘米，它的周长是多少厘米？
<gadget id="calculator">7 + 3</gadget>
<output>10</output>

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

<result>20</result>