There is a pile of coal in the cafeteria. It was originally planned to burn 90 kilograms per day, which can last for 30 days. If 15 kg is saved every day, how many more days can this pile of coal be burned?
食堂有一堆煤，原计划每天烧90千克，可以烧30天．若每天节约15千克，这堆煤可多烧多少天？
<gadget id="calculator">90 * 30</gadget>
<output>2_700</output>

<gadget id="calculator">90 - 15</gadget>
<output>75</output>

<gadget id="calculator">2_700 / 75</gadget>
<output>36</output>

<gadget id="calculator">36 - 30</gadget>
<output>6</output>

<result>6</result>