Master Zhang processes a batch of parts. If he processes 60 parts per day, he needs to postpone the completion by 2 days. If he processes 75 parts per day, he can complete it one day earlier. How many parts are in this batch?
张师傅加工一批零件，如果每天加工60个，就要延期2天完成，如果每天加工75个，则可提前一天完成，这批零件多少个．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">1 / 60</gadget>
<output>1/60 = around 0.016667</output>

<gadget id="calculator">1 / 75</gadget>
<output>1/75 = around 0.013333</output>

<gadget id="calculator">(1/60) - (1/75)</gadget>
<output>1/300 = around 0.003333</output>

<gadget id="calculator">3 / (1/300)</gadget>
<output>900</output>

<result>900</result>