There is a pile of coal that was originally planned to burn 105 kilograms per day, and it can be burned for 30 days. After improving the technology, it burns 15 kilograms less per day. How many more days can this pile of coal be burned? (Solve using ratio method)
有一堆煤原计划每天烧105千克，可以烧30天，改进技术后，每天少烧15千克，这堆煤可以多烧几天？(用比例方法解答)
<gadget id="calculator">30 * 15</gadget>
<output>450</output>

<gadget id="calculator">105 * 30</gadget>
<output>3_150</output>

<gadget id="calculator">30 * 105</gadget>
<output>3_150</output>

<gadget id="calculator">3_150 - 3_150</gadget>
<output>0</output>

<gadget id="calculator">450 + 0</gadget>
<output>450</output>

<gadget id="calculator">105 - 15</gadget>
<output>90</output>

<gadget id="calculator">450 / 90</gadget>
<output>5</output>

<result>5</result>