Bus A and Bus B leave the bus depot at 4 pm. Bus A takes 15 minutes to do its route and bus B takes 35 minutes to complete its route. At what time are they both back at the bus depot together? Give your answer as a 12-hour clock time.

An automobile assembly line operation has a scheduled mean completion time, μ, of 12 minutes. the standard deviation of completion times is 1.6 minutes. it is claimed that, under new management, the mean completion time has decreased. to test this claim, a random sample of 33 completion times under new management was taken. the sample had a mean of 11.2 minutes. assume that the population is normally distributed. can we support, at the 0.05 level of significance, the claim that the mean completion time has decreased under new management? assume that the standard deviation of completion times has not changed.