The master received a batch of production tasks for parts and planned to complete them in 9 hours. After the master gave birth for 2 hours, the apprentice came to help, so the two worked together for another 4 hours to complete all the tasks. It is known that the apprentice can produce 28 parts per hour. How many parts are there in this batch?
师傅接到一批零件的生产任务，计划9小时完成．师傅生产2小时后，徒弟赶来帮忙，这样两人又共同生产了4小时完成了全部任务．已知徒弟每小时能生产28个零件，这批零件共有多少个？
<gadget id="calculator">2 + 4</gadget>
<output>6</output>

<gadget id="calculator">9 - 6</gadget>
<output>3</output>

<gadget id="calculator">4 / 3</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">28 * (4/3) * 9</gadget>
<output>336</output>

<result>336</result>