A metal bucket without a cover is 4dm in height and 2.5dm in length and width. How many square decimeters of iron are needed to make a pair of such buckets?
一种不带盖的铁皮水桶，高4dm，长、宽都是2.5dm，做一对这样的水桶至少要用铁皮多少平方分米？
<gadget id="calculator">2.5 * 2.5</gadget>
<output>6.25</output>

<gadget id="calculator">2.5 * 4 * 4</gadget>
<output>40</output>

<gadget id="calculator">6.25 + 40</gadget>
<output>46.25</output>

<result>46.25</result>