Master Wang processes a batch of parts. If the work efficiency is increased by 20%, it can be completed 1 hour earlier. If the original efficiency is used to make 210 parts first, and then the efficiency is increased by 25%, it can be completed (4/5) hours earlier. How many parts are there in this batch?
王师傅加工一批零件，如果工作效率提高20%，则可提前1小时完成，如按原效率先做210个零件后，再将效率提高25%，则可提前(4/5)小时完成，求这批零件有多少个？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">1 / (6/5)</gadget>
<output>5/6 = around 0.833333</output>

<gadget id="calculator">1 - (5/6)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / (1/6)</gadget>
<output>6</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">1 / (5/4)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 / (5/4) / (1/5)</gadget>
<output>4</output>

<gadget id="calculator">6 - 4</gadget>
<output>2</output>

<gadget id="calculator">210 / 2</gadget>
<output>105</output>

<gadget id="calculator">105 * 6</gadget>
<output>630</output>

<result>630</result>