A job is completed by A alone in 8 hours. After A and B cooperate for 3 hours, A leaves beforehand, and B completes it by himself for 42 hours. How many hours does it take for B alone to complete this job?
一件工作甲独做8小时完成，甲乙合作3小时后，甲有事先走了，由乙又独做42小时完成，这项工作由乙一人去做几小时完成？
<gadget id="calculator">42 + 3</gadget>
<output>45</output>

<gadget id="calculator">3 / 8</gadget>
<output>3/8 = around 0.375</output>

<gadget id="calculator">1 - (3/8)</gadget>
<output>5/8 = around 0.625</output>

<gadget id="calculator">45 / (5/8)</gadget>
<output>72</output>

<result>72</result>