To process a batch of parts, the two teams cooperate to complete it in 12 hours, if Team A does it alone in 20 hours. When the cooperation is completed, team B processes 1200 parts less than team A. How many parts did Team A make in total?
加工一批零件，两队合作12小时完成，如果甲队单独做20小时完成．合作完成时，乙队比甲队少加工1200个零件．请问甲队共做了多少个零件．
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) * 12</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">1 - (3/5)</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">1_200 / (1/5)</gadget>
<output>6_000</output>

<gadget id="calculator">6_000 * (1/20) * 12</gadget>
<output>3_600</output>

<result>3_600</result>