A rectangular skating rink is 30 meters long and 20 meters wide, with railings around it. How long is the railing?
一个长方形溜冰场长30米，宽20米，在四周围上栏杆，栏杆长多少米？
<gadget id="calculator">30 + 20</gadget>
<output>50</output>

<gadget id="calculator">50 * 2</gadget>
<output>100</output>

<result>100</result>