One task, A alone takes 12 days to complete, and B alone takes 15 days to complete. During the process of their cooperation, A has to leave for a few days due to something. Therefore, this job took 10 days to complete the task in the end. Ask A How many days have you been doing it?
一件工作，甲单独做要12天完成，乙单独做要15天完成，在他们合作的过程中，甲因有事而离开几天，因此，这件工作最后共用了10天才完成任务，求甲做了几天？
<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">10 * (1/15)</gadget>
<output>2/3 = around 0.666667</output>

<gadget id="calculator">1 - (2/3)</gadget>
<output>1/3 = around 0.333333</output>

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

<gadget id="calculator">(1/3) / (1/12)</gadget>
<output>4</output>

<result>4</result>