A pile of coal was originally planned to burn 3 tons per day, which can last for 72 days. After improving the technology, burn 2.4 tons per day. How many days can this pile of coal burn now? (Solution with proportional knowledge)
一堆煤原计划每天烧3吨，可以烧72天．改进技术后，每天烧2.4吨．这堆煤现在可烧多少天？(用比例知识解)
<gadget id="calculator">72 * 3</gadget>
<output>216</output>

<gadget id="calculator">216 / 2.4</gadget>
<output>90</output>

<result>90</result>