A batch of parts A can be completed in 24 hours alone, and B can be completed in 30 hours alone. Now the two work together to increase the speed (1/3). When all (1/5) are completed, 21 fewer pieces are done per hour. As a result, if it takes 12 hours, how many parts are there?
一批零件甲单独做24小时完成，乙单独故30小时完成，现在两人合作，提速(1/3)．完成全部的(1/5)时，每小时少做21件．结果共用12小时，则共多少零件？
<gadget id="calculator">1 / 24</gadget>
<output>1/24 = around 0.041667</output>

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

<gadget id="calculator">(1/24) + (1/30)</gadget>
<output>3/40 = around 0.075</output>

<gadget id="calculator">1 / 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">1 + (1/3)</gadget>
<output>4/3 = around 1.333333</output>

<gadget id="calculator">(3/40) * (4/3)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(1/5) / (1/10)</gadget>
<output>2</output>

<gadget id="calculator">12 - 2</gadget>
<output>10</output>

<gadget id="calculator">(4/5) / 10</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">(1/10) - (2/25)</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">21 / (1/50)</gadget>
<output>1_050</output>

<result>1_050</result>