Two identical projects are completed by A alone in 6 hours, and by B alone in 9 hours. B works for 1 hour first, and A does it again. After how many hours, both of them have done the same amount?
两项一样的工程甲单独做6小时完成，乙单独做9小时完成，乙先做1小时，甲再做，几小时后两人做的同样多？
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) - (1/9)</gadget>
<output>1/18 = around 0.055556</output>

<gadget id="calculator">(1/9) / (1/18)</gadget>
<output>2</output>

<result>2</result>