What is the eleventh term of an arithmetic sequence in which a1=3 and d=6

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Write an inequality and solve each problem.for exercises 11 and 12, interpret the solution.

What is the axis of symmetry of the function f(x)=-(x+ 9)(x-21)

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.