Master Gao made 168 parts in 8 hours, and Master Wang made 196 parts in 7 hours. How many parts per hour does Master Gao make less than Master Wang?
高师傅8小时做了168个零件，王师傅7小时做了196个零件．高师傅比王师傅平均每小时少做多少个零件？
<gadget id="calculator">196 / 7</gadget>
<output>28</output>

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

<gadget id="calculator">28 - 21</gadget>
<output>7</output>

<result>7</result>