For a batch of parts, master Zhang will complete it in 20 hours, and master Wang will complete it in 30 hours. If two people do it at the same time, Master Zhang will make 60 more parts than Master Wang when completing the task. How many parts are there in this batch?
一批零件，张师傅独做20时完成，王师傅独做30时完成．如果两人同时做，那么完成任务时张师傅比王师傅多做60个零件．这批零件共有多少个？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">1 / (1/12)</gadget>
<output>12</output>

<gadget id="calculator">12 / 20</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">12 / 30</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(3/5) - (2/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">60 / (1/5)</gadget>
<output>300</output>

<result>300</result>