Question 1189402
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Machine A worked 4 hours and completed 4/10 of the job.  6/10 of the job left.


Machine B completed remaining 6/10 of the job  in  {{{((6/10))/((1/12))}}} = {{{72/10}}} = 7.2  hours = 7 hours and 12 minutes.


Since machine B started at 9 am, it completed the job at 4:12 pm.    <U>ANSWER</U>
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Solved.