rectangular vegetable field is 20 meters long and 20 meters wide. If you want to fence this vegetable field, how long is the fence?
一块长方形菜地，长20米，宽20米．如果要给这块菜地围上篱笆，篱笆的长是多少米？
<gadget id="calculator">20 + 20</gadget>
<output>40</output>

<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<result>80</result>