Let μ denote the true average tread life of a certain type of tire. Consider testing H0 : μ =20000 versus Ha : μ >20000 based on a sample of size n = 16 from a normal population distribution with σ = 1500. A test with α = .01 is used. (z.01 = 2.33, z.1 = 1.28) (a) If ¯ x = 20960, what is the decision? (b) What is the probability of making a type II error when μ = 21000? (c) If it is also required that β (21000)=.1, what sample size n is necessary?