There are several workers on a production line in a certain factory to produce a batch of parts. When each worker is working in his original position, the task can be completed in 9 hours. If the positions of two of them are exchanged at will, the production efficiency of the others remains the same, and the task can be completed 1 hour earlier. It is known that the production of this batch of parts is (45/7) hours earlier. How many of these workers exchange jobs in pairs?
某工厂的一条生产线有若干工人，生产一批零件，当每个工人都在自己原来的岗位工作时，9小时可以完成任务．如果任意交换其中两人的岗位，其他人生产效率不变，可提前1小时完成任务，现知生产这批零件共提前(45/7)小时．其中有多少工人两两同时交换了岗位？
<gadget id="calculator">45 / 7</gadget>
<output>45/7 = around 6.428571</output>

<gadget id="calculator">9 - (45/7)</gadget>
<output>18/7 = around 2.571429</output>

<gadget id="calculator">1 / (18/7)</gadget>
<output>7/18 = around 0.388889</output>

<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(7/18) - (1/9)</gadget>
<output>5/18 = around 0.277778</output>

<gadget id="calculator">1 / 8</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">(1/8) - (1/9)</gadget>
<output>1/72 = around 0.013889</output>

<gadget id="calculator">(5/18) / (1/72)</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<result>40</result>