The length of the rectangle is 7 meters, the width is 3 meters, what is the circumference in meters?
长方形的长是7米，宽是3米，周长是多少米．
<gadget id="calculator">7 + 3</gadget>
<output>10</output>

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

<result>20</result>