A random sample ofnmeasurements was selected from a population with unknown mean and standard deviation . Calculate a99% confidence interval forfor each of the following situations:

(a)n=85,x=23.8,s=3.75

(b)n=120,x=62.7,s=4.52

(c)n=80,x=50.6,s=2.67

(d)n=85,x=91,s=2.73