It takes 9 hours for A to complete a job alone, and B’s work efficiency is three times that of A. If they cooperate at the same time, how many hours can they complete the job?
一件工作甲单独完成需要9小时，乙的工作效率是甲的3倍，两人同时合作，几小时能完成工作？
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/9) * 3</gadget>
<output>1/3 = around 0.333333</output>

<gadget id="calculator">(1/9) + (1/3)</gadget>
<output>4/9 = around 0.444444</output>

<gadget id="calculator">1 / (4/9)</gadget>
<output>9/4 = around 2.25</output>

<result>9/4 = around 2.25</result>