It takes 10 hours for A and B to do a job together, and 15 hours for B to do it alone. How many hours will it take for A to do this job alone?
一件工作，甲乙合做要用10小时，乙单独做要用15小时，这件工作如果由甲单独做要几小时？
<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>1/30 = around 0.033333</output>

<gadget id="calculator">1 / (1/30)</gadget>
<output>30</output>

<result>30</result>