A rectangular vegetable field is 19 meters long and 15 meters wide, surrounded by a fence. How long is the fence?
一块长方形菜地，长19米，宽15米，四周围上篱笆，篱笆长多少米？
<gadget id="calculator">19 + 15</gadget>
<output>34</output>

<gadget id="calculator">34 * 2</gadget>
<output>68</output>

<result>68</result>