If the length and width of a rectangle are 15 decimeters and 5 decimeters respectively, what is its perimeter in meters?
一个长方形的长和宽分别是15分米和5分米，它的周长是多少米．
<gadget id="calculator">15 + 5</gadget>
<output>20</output>

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

<result>40</result>