To process a batch of parts, A and B cooperate to complete it in 5 hours, and A alone completes it in 9 hours. It is known that A processes 2 more parts per hour than B, how many parts are there in this batch?
加工一批零件，甲乙合作5小时完成，甲独做9小时完成．已知甲每小时比乙多加工2个零件，这批零件共有多少个？
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/5) - (1/9)</gadget>
<output>4/45 = around 0.088889</output>

<gadget id="calculator">(1/9) - (4/45)</gadget>
<output>1/45 = around 0.022222</output>

<gadget id="calculator">2 / (1/45)</gadget>
<output>90</output>

<result>90</result>