What is the perimeter of a rectangle with a length of 30 meters and a width of 20 meters?
长是30米，宽是20米的长方形周长是多少米．
<gadget id="calculator">30 + 20</gadget>
<output>50</output>

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

<result>100</result>