Master Zhang needs to process 72 parts, 18 of which have already been processed, and 6 parts are processed per hour. How many hours are required to complete the processing, and what is the comprehensive formula listed.
张师傅要加工72个零件，已经加工了18个，每小时加工6个，要求还要多少小时能加工完，列出综合算式是多少．
<gadget id="calculator">72 - 18</gadget>
<output>54</output>

<gadget id="calculator">54 / 6</gadget>
<output>9</output>

<result>9</result>