The length of a rectangle is 12 decimeters, and the width is 4 decimeters shorter than the length. What is the perimeter?
一个长方形的长是12分米、宽比长短了4分米，周长是多少分米？
<gadget id="calculator">12 - 4</gadget>
<output>8</output>

<gadget id="calculator">12 + 8</gadget>
<output>20</output>

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

<result>40</result>