To complete the job 6*10=60 man/hours are needed.
By 5:00 PM 6*6=36 man/hour done. 24 is left.
5:00 PM - 6:00 PM 7 man/hour; ->36+7=43
6:00 PM - 7:00 PM 8 man/hour; ->43+8=51
7:00 PM - 8:00 PM 9 man/hour. ->51+9=60(work completed)
Hence,Option(D)8:00 pm.