The engineering team repaired a section of road. The original plan was to repair 3.2 kilometers per day, and it was completed in 15 days. In fact, an extra 0.8 kilometers was repaired per day. How many days can the repair be completed in advance? (Solve with ratio)
工程队修一段公路，原计划每天修3.2千米，15天完成，实际每天多修0.8千米，可以提前几天修完？(用比例解)
<gadget id="calculator">3.2 * 15</gadget>
<output>48</output>

<gadget id="calculator">0.8 * 15</gadget>
<output>12</output>

<gadget id="calculator">12 - 48</gadget>
<output>-36</output>

<gadget id="calculator">48 + (-36)</gadget>
<output>12</output>

<gadget id="calculator">3.2 + 0.8</gadget>
<output>4</output>

<gadget id="calculator">12 / 4</gadget>
<output>3</output>

<result>3</result>