To produce a batch of parts, A and B work together for 12 hours. It is known that the ratio of work efficiency between A and B is 2:3. How many hours does it take for B to produce this batch of parts alone?
生产一批零件，甲乙二人合作用12小时，已知甲乙二人的工作效率之比是2：3，乙单独生产这批零件要用多少小时．
<gadget id="calculator">1 / 12</gadget>
<output>1/12 = around 0.083333</output>

<gadget id="calculator">2 + 3</gadget>
<output>5</output>

<gadget id="calculator">3 / 5</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">(1/12) * (3/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / (1/20)</gadget>
<output>20</output>

<result>20</result>