A job alone takes 10 days to complete, and B alone takes 15 days to complete. After A and B worked together for 3 days, A left due to business, and then B continued to finish the work. How many days did B work in total?
一件工作，甲单独做要10天完成，乙单独做要15天完成．甲、乙2人合做了3天后，甲因事离开，接着由乙继续做完，乙一共做了多少天？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 15</gadget>
<output>1/15 = around 0.066667</output>

<gadget id="calculator">(1/10) + (1/15)</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">(1/6) * 3</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">1 - (1/2)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">(1/2) / (1/15)</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">(15/2) + 3</gadget>
<output>21/2 = around 10.5</output>

<result>21/2 = around 10.5</result>