Master Zhang made 168 parts in 8 hours, and Master Li made 120 parts in 5 hours. How many parts does Master Zhang make less per hour than Master Li?
张师傅8小时做了168个零件，李师傅5小时做了120个零件．张师傅比李师傅平均每小时少做多少个零件？
<gadget id="calculator">120 / 5</gadget>
<output>24</output>

<gadget id="calculator">168 / 8</gadget>
<output>21</output>

<gadget id="calculator">24 - 21</gadget>
<output>3</output>

<result>3</result>