It takes Master Zhang 30 hours to process a batch of parts alone, and Master Li processes 20 per hour. Now the two work together. When the work is completed, Master Zhang will do 20% more than Master Li. How many parts are there in this batch?
单独加工一批零件，张师傅需要30小时，李师傅每小时加工20个，现在两人合作，完工时，张师傅比李师傅多做全部的20%，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">(6/5) / 2</gadget>
<output>3/5 = around 0.6</output>

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

<gadget id="calculator">(3/5) / (1/30)</gadget>
<output>18</output>

<gadget id="calculator">1 - (3/5)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">18 / (2/5)</gadget>
<output>45</output>

<gadget id="calculator">20 * 45</gadget>
<output>900</output>

<result>900</result>