A batch of parts is completed separately, A takes 20 days, and B takes 30 days. The two worked together for 7 days, and there are still 360 parts left to be finished. How many parts are there in this batch?
一批零件，单独完成，甲要20天，乙要30天．两人合做7天，还剩360个没有做完，这批零件共有多少个？
<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

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

<gadget id="calculator">(1/20) + (1/30)</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/12) * 7</gadget>
<output>7/12 = around 0.583333</output>

<gadget id="calculator">1 - (7/12)</gadget>
<output>5/12 = around 0.416667</output>

<gadget id="calculator">360 / (5/12)</gadget>
<output>864</output>

<result>864</result>