Suppose that you wish to estimate the mean life of automobile tires. A random sample of n = 18 tires has been taken and the sample mean has been found to be 58,600 miles with a sample standard deviation of 12,400 miles. Assume the life of tires is roughly normally distributed. a. Calculate and interpret a 90% confidence interval for the true mean life of automobile tires. b. Calculate and interpret a 95% confidence interval for the true mean life of automobile tires. a. Find the values of t with R b. Calculate the interval in R c. Which interval is more precise? Why?