If you enclose a rectangular vegetable field with a length of 20 meters and a width of 8 meters, what is its perimeter in meters?
如果围一块长20米、宽8米的长方形菜地，它的周长是多少米？
<gadget id="calculator">20 + 8</gadget>
<output>28</output>

<gadget id="calculator">28 * 2</gadget>
<output>56</output>

<result>56</result>