If A alone completes a project, A needs 10 hours. If two people work together, it can be completed in 6 hours. How many hours does B need to complete alone?
一项工程，若甲单独完成，甲需要10小时，如果两人合作，6小时就能完成，乙单独完成需要多少小时．
<gadget id="calculator">1 / 6</gadget>
<output>1/6 = around 0.166667</output>

<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/6) - (1/10)</gadget>
<output>1/15 = around 0.066667</output>

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

<result>15</result>