To make a cuboid iron box without a cover, its length is 2.5 decimeters, its width and height are both 1.5 decimeters, at least how many square decimeters of iron sheet should be used.
做一个无盖的长方体铁盒，它的长是2.5分米，宽和高都是1.5分米，至少要用多少平方分米的铁皮．
<gadget id="calculator">2.5 * 1.5</gadget>
<output>3.75</output>

<gadget id="calculator">1.5 * 1.5</gadget>
<output>2.25</output>

<gadget id="calculator">3.75 + 3.75 + 2.25</gadget>
<output>9.75</output>

<gadget id="calculator">9.75 * 2</gadget>
<output>19.5</output>

<gadget id="calculator">19.5 - 3.75</gadget>
<output>15.75</output>

<result>15.75</result>