The master processes 90 parts per hour, the apprentice processes a less parts per hour than the master, and how many parts does the apprentice process in 3 hours.
师傅每小时加工90个零件，徒弟每小时比师傅少加工a个零件，徒弟3小时加工多少个零件．
<gadget id="calculator">270 - 3</gadget>
<output>267</output>

<result>267</result>