To make 10 cuboid iron chimneys, each section is 20 decimeters long, 4 decimeters wide, and 3 decimeters high, how many square meters of iron sheets should be used at least?
做10节长方体的铁皮烟囱，每节长20分米，宽4分米，高3分米，至少用多少平方米的铁皮？
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<gadget id="calculator">60 + 80</gadget>
<output>140</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">140 * 2 * (1/10)</gadget>
<output>28</output>

<result>28</result>