A random sample was selected from a population having a normal distribution. Calculate a 90% confidence interval estimate for for each of the following situations:
a. Σx = 134, n = 10, s = 3.1
b. Σx = 3,744, n = 120, s = 8.2
c. Σx = 40.5, n = 9, σ = 2.9
d. Σx = 585.9, Σx2 = 15,472.37, n = 27