job is completed in 12 days alone, and B is completed in 9 days alone. First, A works for a few days, and B continues to do it. It takes 10 days to complete the work. How many days does A do?
一工作甲独做12天完工，乙单独做9天完工，先甲做几天，乙再接着做，共用10天完工，甲做了几天？
<gadget id="calculator">1 / 9</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">(1/9) * 10</gadget>
<output>10/9 = around 1.111111</output>

<gadget id="calculator">(10/9) - 1</gadget>
<output>1/9 = around 0.111111</output>

<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">(1/9) - (1/12)</gadget>
<output>1/36 = around 0.027778</output>

<gadget id="calculator">(1/9) / (1/36)</gadget>
<output>4</output>

<result>4</result>