A pile of coal, originally planned to burn 15 tons per day, can be burned for 40 days. Actually saved 3 tons per day than the original plan, how many days did it actually burn?
一堆煤，原计划每天烧15吨，可烧40天．实际每天比原计划节约3吨，实际烧了多少天？
<gadget id="calculator">15 * 40</gadget>
<output>600</output>

<gadget id="calculator">15 - 3</gadget>
<output>12</output>

<gadget id="calculator">600 / 12</gadget>
<output>50</output>

<result>50</result>