It is 28 decimeters to make a positive shape nozzle perimeter, and 12 ventilation pipes of 20 decimeters, how many square meters of iron sheet are needed at least?
要做一个正才形管口周长是28分米，长20分米的通气管子12根，至少需要铁皮多少平方米？
<gadget id="calculator">12 / 100</gadget>
<output>3/25 = around 0.12</output>

<gadget id="calculator">28 * 20 * (3/25)</gadget>
<output>336/5 = around 67.2</output>

<result>336/5 = around 67.2</result>