Master Zhang makes 160 parts in 8 hours, and Master Wang makes 120 parts in 4 hours. On average, how many parts does Master Zhang make less than Master Wang per hour?
张师傅8小时做160个零件，王师傅4小时做120个零件，张师傅比王师傅平均每小时少做多少个零件？
<gadget id="calculator">120 / 4</gadget>
<output>30</output>

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

<gadget id="calculator">30 - 20</gadget>
<output>10</output>

<result>10</result>