There is a rectangular field with a length of 20 meters and a width of 15 meters. How many meters of fence are needed to fence around the land?
有一块长方形地，长是20米，宽是15米．要在这块地的四周围上篱笆，一共需要篱笆多少米？
<gadget id="calculator">20 + 15</gadget>
<output>35</output>

<gadget id="calculator">35 * 2</gadget>
<output>70</output>

<result>70</result>