A project can be completed in 10 days alone, and B can be completed in 15 days alone. Now A and B cooperate, but because B has rested for several days, it takes 8 days to complete it. How many days did B rest?
一项工程，甲单独做10日可以完成，乙单独做15日可以完成，今甲乙合作，但因乙休息了若干日，则用了八日完成，问乙休息了几天？
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * 8</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">1 - (4/5)</gadget>
<output>1/5 = around 0.2</output>

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

<gadget id="calculator">(1/5) / (1/15)</gadget>
<output>3</output>

<gadget id="calculator">8 - 3</gadget>
<output>5</output>

<result>5</result>