The standard deviation for a population is = 15.3. A sample of 36 observations selected from

The standard deviation for a population is σ = 15.3. A sample of 36 observations selected from this population gave a mean equal to 74.8.
a. Make a 90% confidence interval for µ.
b. Construct a 95% confidence interval for µ.
c. Determine a 99% confidence interval for µ.
d. Does the width of the confidence intervals constructed in parts a through c increase as the confidence level increases? Explain your answer.