A cuboid packing box is 40 cm long, 25 cm wide, and 6 cm high. How many square meters of cardboard should be used to make such a packing box?
一个长方体包装盒，长40厘米，宽25厘米，高6厘米，做一个这样的包装盒至少要用多少平方米的硬纸板．
<gadget id="calculator">40 * 25</gadget>
<output>1_000</output>

<gadget id="calculator">40 * 6</gadget>
<output>240</output>

<gadget id="calculator">25 * 6</gadget>
<output>150</output>

<gadget id="calculator">1_000 + 240 + 150</gadget>
<output>1_390</output>

<gadget id="calculator">1 * 10_000</gadget>
<output>10_000</output>

<gadget id="calculator">2 / 10_000</gadget>
<output>1/5_000 = around 0.0002</output>

<gadget id="calculator">1_390 * (1/5_000)</gadget>
<output>139/500 = around 0.278</output>

<result>139/500 = around 0.278</result>