A random sample of n = 36 observations has a mean a = 28.1 and a standard deviation s = 3.8. (a) Find a 90% confidence interval for J. (Round your answers to three decimal places.) (b) Find a 90% lower confidence bound for the population mean u. (Round your answer to three decimal places.) (c) At least how many observations do you need to estimate / to within a margin of error of 0.5, with probability equal to 0.95? Use the standard deviation from this current study