For a batch of parts, Xiao Wang needs to make 15 parts per hour, and it takes 8 hours to complete. If he makes 20 parts per hour, how many hours will it take to complete? (use solution ratio)
一批零件，小王每小时做要15个零件，要8小时完成，如果每小时做20个零件，需要几小时完成？(用解比例)
<gadget id="calculator">15 * 8</gadget>
<output>120</output>

<gadget id="calculator">120 / 20</gadget>
<output>6</output>

<result>6</result>