A worker processes a batch of parts, plans to process 20 parts per hour, and finishes processing in 12 hours. If 4 more parts are processed per hour, how many hours can it be completed in advance?
一个工人加工一批零件，计划每小时加工20个，12小时加工完，如果每小时多加工4个，可以提前几小时完成？
<gadget id="calculator">20 + 4</gadget>
<output>24</output>

<gadget id="calculator">12 / 24</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">20 * (1/2)</gadget>
<output>10</output>

<gadget id="calculator">12 - 10</gadget>
<output>2</output>

<result>2</result>