A rectangular playground is 30 meters long and 20 meters wide. If you run 2 laps around the playground, how many meters will you run?
一个长方形操场长30米，宽20米，绕着这个操场跑2圈，跑了多少米．
<gadget id="calculator">30 + 20</gadget>
<output>50</output>

<gadget id="calculator">50 * 2 * 2</gadget>
<output>200</output>

<result>200</result>