What is the formula for this? i need with this really badly

What is the value of the expression 9+n/3-6 when n = 12? 1. 5. 7. 12.

Which of the following is the explicit rule for a geometric sequence defined a recursive formula of a -5a for which the first term is 23?

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.