A rectangular piece of glass is 12 decimeters long and 8 decimeters wide, what is its perimeter?
一块长方形玻璃长是12分米，宽是8分米，它的周长是多少．
<gadget id="calculator">12 + 8</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>