Processing a batch of parts, A and B can complete it in 12 days, and B can complete it in 20 days alone. When A and B cooperate to complete the task, if B gives A 87, then the number of parts of the two is equal. Find this batch What is the total number of parts?
加工一批零件，甲、乙合做12天可以完成，乙独做20天可以完成，甲、乙合作完成任务时，乙如果给甲87个，那么两人的零件个数相等，求这批零件的总数是多少个？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) - (1/20)</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">12 * (1/30)</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">2 / (1/5)</gadget>
<output>10</output>

<gadget id="calculator">87 * 10</gadget>
<output>870</output>

<result>870</result>