If the length of a rectangle is 10 decimeters and its width is 5 decimeters less than its length, what is its perimeter?
长方形的长是10分米，宽比长少5分米，它的周长是多少分米．
<gadget id="calculator">10 - 5</gadget>
<output>5</output>

<gadget id="calculator">5 + 10</gadget>
<output>15</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<result>30</result>