If the length of a rectangle is 12 decimeters and the width is 7 decimeters, what is its perimeter?
一个长方形的长是12分米，宽是7分米，它的周长是多少分米．
<gadget id="calculator">12 + 7</gadget>
<output>19</output>

<gadget id="calculator">19 * 2</gadget>
<output>38</output>

<result>38</result>