Uncle Zhang made a cuboid wooden box (without a cover) for selling apples. It is 60 cm long, 40 cm wide, and 30 cm high. How many planks at least square meters are used to make this kind of box?
张大爷制作了一种卖苹果用的长方体木箱(无盖)，它的长是60厘米，宽40厘米，高30厘米．做这种箱子至少用多少木板至少平方米？
<gadget id="calculator">60 * 30</gadget>
<output>1_800</output>

<gadget id="calculator">40 * 30</gadget>
<output>1_200</output>

<gadget id="calculator">1_800 + 1_200</gadget>
<output>3_000</output>

<gadget id="calculator">3_000 * 2</gadget>
<output>6_000</output>

<gadget id="calculator">60 * 40</gadget>
<output>2_400</output>

<gadget id="calculator">6_000 + 2_400</gadget>
<output>8_400</output>

<gadget id="calculator">8_400 / 10_000</gadget>
<output>21/25 = around 0.84</output>

<result>21/25 = around 0.84</result>