It takes 8 high school students, working at identical constant individual rates, 10 hours to paint a certain house. At what time will the house be fully painted if 8 students start painting at 9:00 am and one student, working at the same rate, is added per hour starting at 5:00 pm? Choices.
A) 6:06 pm
B) 6:12 pm
C) 6:24 pm
D) 6:42 pm
E) 6:56 pm
Each student paints at a rate of 1/80 of the house per hour.   In 8 hours, the 8 students can paint 64/80 of the house.   From 5 pm to 6 pm, 9 students paint another 9/80 for a total of 73/80.   10 students can paint the remaining 7/80 of the house in 7/10 of an hour = 42 minutes.   The house is completed at 6:42 pm.   The answer is 6:42 pm.
<result>D</result>
It takes 8 high school students, working at identical constant individual rates, 10 hours to paint a certain house. At what time will the house be fully painted if 8 students start painting at 9:00 am and one student, working at the same rate, is added per hour starting at 5:00 pm?