The farmer uncle has a rectangular vegetable field with a length of 8 meters and a width of 5 meters, surrounded by fences, how long is the fence?
农民伯伯有一块长8米，宽5米的长方形菜地，四周围篱笆，篱笆长多少米？
<gadget id="calculator">8 + 5</gadget>
<output>13</output>

<gadget id="calculator">13 * 2</gadget>
<output>26</output>

<result>26</result>