A rectangular vegetable field is 20 meters long and 10 meters wide. What is the perimeter of this vegetable field?
一块长方形菜地，长20米，宽10米，这块菜地的周长是多少米？
<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">30 * 2</gadget>
<output>60</output>

<result>60</result>