There is a parallelogram-shaped flower bed, and the lengths of the two adjacent sides are 12 meters and 9 meters. Now a fence is going to be built around the flower bed. What is the length of the fence in meters?
有一个平行四边形的花坛，相邻两边的长度是12米和9米，现在要在花坛四周围上栅栏，栅栏的长度是多少米？
<gadget id="calculator">12 + 9</gadget>
<output>21</output>

<gadget id="calculator">21 * 2</gadget>
<output>42</output>

<result>42</result>