If a road is repaired by 20 meters per day, it can be completed in 15 days; if it is repaired by 10 meters per day, how many days can it be completed in advance?
一条公路，如果每天修20米，15天修完；如果每天多修10米，可以提前几天修完？
<gadget id="calculator">20 * 15</gadget>
<output>300</output>

<gadget id="calculator">20 + 10</gadget>
<output>30</output>

<gadget id="calculator">300 / 30</gadget>
<output>10</output>

<gadget id="calculator">15 - 10</gadget>
<output>5</output>

<result>5</result>