factory has a pile of coal. If it burns 0.8 tons per day, it can be burned for 30 days. If it saves 0.2 tons per day, how many more days can it be burned? (Solve with ratio)
某工厂有一堆煤，如果每天烧0.8吨，可以烧30天，如果每天节约0.2吨，可以多烧多少天？(用比例解)
<gadget id="calculator">0.8 * 30</gadget>
<output>24</output>

<gadget id="calculator">0.8 - 0.2</gadget>
<output>0.6</output>

<gadget id="calculator">24 / 0.6</gadget>
<output>40</output>

<gadget id="calculator">40 - 30</gadget>
<output>10</output>

<result>10</result>