A rectangular desk calendar whose length is 5 decimeters and whose width is 2 decimeters less than its length, find its perimeter.
一个长方形台历，长是5分米，宽比长少2分米，求出它的周长．
<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">5 + 3</gadget>
<output>8</output>

<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<result>16</result>