A rectangle is 30 meters long and 20 decimeters wide, what is its perimeter?
一个长方形长30米，宽20分米，它的周长是多少分米．
<gadget id="calculator">30 * 10</gadget>
<output>300</output>

<gadget id="calculator">300 + 20</gadget>
<output>320</output>

<gadget id="calculator">320 * 2</gadget>
<output>640</output>

<result>640</result>