The master and apprentice worked together to process 270 parts in 4.5 hours. The master processes 45 pieces per hour on average, how many pieces does the apprentice process on average per hour?
师徒二人4.5小时共同加工了270个零件．师傅平均每小时加工45个，徒弟平均每小时加工多少个？
<gadget id="calculator">45 * 4.5</gadget>
<output>202.5</output>

<gadget id="calculator">270 - 202.5</gadget>
<output>67.5</output>

<gadget id="calculator">67.5 / 4.5</gadget>
<output>15</output>

<result>15</result>