How many square meters of cardboard are needed to make 100 cuboid cartons (without covers), 40 decimeters long, 30 decimeters wide, and 20 decimeters high?
做100个长方体纸箱(无盖)，长40分米，宽30分米，高20分米，需要多少平方米的纸板？
<gadget id="calculator">40 * 30</gadget>
<output>1_200</output>

<gadget id="calculator">30 * 20</gadget>
<output>600</output>

<gadget id="calculator">20 * 40</gadget>
<output>800</output>

<gadget id="calculator">1_200 + 600 + 800</gadget>
<output>2_600</output>

<gadget id="calculator">2_600 * 2</gadget>
<output>5_200</output>

<gadget id="calculator">5_200 - 1_200</gadget>
<output>4_000</output>

<gadget id="calculator">100 / 100</gadget>
<output>1</output>

<gadget id="calculator">4_000 * 1</gadget>
<output>4_000</output>

<result>4_000</result>