A batch of parts is jointly produced by A and B. A has completed (3/7) of this batch of parts, and B has completed 120 more parts than A. How many parts are there in total?
一批零件，甲乙合做，甲完成了这批零件的(3/7)，乙比甲多完成120个，这批零件一共有多少个？
<gadget id="calculator">3 / 7</gadget>
<output>3/7 = around 0.428571</output>

<gadget id="calculator">1 - (3/7) - (3/7)</gadget>
<output>1/7 = around 0.142857</output>

<gadget id="calculator">120 / (1/7)</gadget>
<output>840</output>

<result>840</result>