A project can be completed in 15 hours with the cooperation of A and B, and 20 hours with the cooperation of B and C. Now, after B firstly works for 32 hours, A and C cooperate for another 3 hours to complete it. If B alone can complete it in a few hours.
一项工程甲乙合作15小时可以完成，乙丙合作20小时可以完成，现在由乙先做32小时后，甲丙又合作了3小时才完成，若单独由乙做几小时可以完成．
<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / (1/40)</gadget>
<output>40</output>

<result>40</result>