The master and the apprentice process a batch of parts at the same time, and it takes (15/4) hours to complete. The master makes 30 more parts than the apprentice. If this batch of parts is processed separately, the master will spend 6 hours, and the apprentice will spend 10 hours. How many parts are there in this batch?
师徒两人同时加工一批零件，用了(15/4)小时完成，师傅比徒弟一共多做30个．如果单独加工这批零件，师傅要用6小时，徒弟要用10小时，这批零件有多少个？
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/6) - (1/10)</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">15 / 4</gadget>
<output>15/4 = around 3.75</output>

<gadget id="calculator">(1/15) * (15/4)</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">30 / (1/4)</gadget>
<output>120</output>

<result>120</result>