Uncle Li's house has a nursery against the wall, the length and width are 18 meters and 12 meters respectively. If bamboo fences surround this rectangular nursery, how many meters of bamboo fences are needed at least?
李大爷家有一块靠墙的苗圃，长和宽分别是18米和12米．如果竹篱笆围这个长方形苗圃，至少需要多少米竹篱笆？
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">18 + 24</gadget>
<output>42</output>

<result>42</result>