Master Zhang made 138 parts in 6 hours, and Master Li made 160 parts in 8 hours. How many more parts per hour did Master Zhang make than Master Li?
张师傅6小时做了138个零件，李师傅8小时做了160个零件，张师傅比李师傅平均每小时多做多少个零件？
<gadget id="calculator">138 / 6</gadget>
<output>23</output>

<gadget id="calculator">160 / 8</gadget>
<output>20</output>

<gadget id="calculator">23 - 20</gadget>
<output>3</output>

<result>3</result>