To produce a batch of parts, it is planned to produce 80 parts per day, and it will be completed in 15 days. In fact, 20 more parts will be produced per day. How many days can it be completed in advance?
生产一批零件，计划每天生产80个，15天完成，实际每天多生产20个，可以提前几天完成？
<gadget id="calculator">80 + 20</gadget>
<output>100</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">80 * (3/20)</gadget>
<output>12</output>

<gadget id="calculator">15 - 12</gadget>
<output>3</output>

<result>3</result>