A batch of coal was shipped from the cafeteria. It is planned to burn 1.8 tons per day, which can be burned for 20 days. In fact, the cafeteria burned 7.2 tons of coal in the first 3 days. Based on this calculation, how many days can this batch of coal be burned?
食堂运来一批煤，计划每天烧1.8吨，可以烧20天，实际食堂前3天烧煤7.2吨，照这样计算，这批煤可以烧多少天？
<gadget id="calculator">1.8 * 20</gadget>
<output>36</output>

<gadget id="calculator">7.2 / 3</gadget>
<output>2.4</output>

<gadget id="calculator">36 / 2.4</gadget>
<output>15</output>

<result>15</result>