You measure the lifetime of a random sample of 64 tires of a certain brand. The sample mean is 2 = 50 months. Suppose that the lifetimes for tires of this brand follow a Normal distribution, with unknown mean je and standard deviation o- 5 months A 99% confidence interval for u is: a. 49.8 to 50.2. b. 48.78 to 51.22. 48.39 to 51.61. d. 40.2 to 59.8.