Use iron sheets to make a cuboid ventilation pipe with a length of 3m, a width of 4dm, and a height of 3dm. How many square meters of iron sheets are needed to make this ventilation pipe?
用铁片做一个长3m，宽4dm，高3dm的长方体通风管，做这个通风管至少需要多少平方米的铁皮？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">3 * (3/10)</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">4 / 10</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">3 * (2/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">(9/10) + (6/5)</gadget>
<output>21/10 = around 2.1</output>

<gadget id="calculator">(21/10) * 2</gadget>
<output>21/5 = around 4.2</output>

<result>21/5 = around 4.2</result>