A hair salon in Cambridge, Massachusetts, reports that on seven randomly selected weekdays, the number of customers who visited the salon were 40, 30, 28, 22, 36, 16, and 50. It can be assumed that weekday customer visits follow a normal distribution.

a. Construct the 90% confidence interval for the average number of customers who visit the salon on weekdays.

b. Construct the 99% confidence interval for the average number of customers who visit the salon on weekdays.

c. What happens to the width of the interval as the confidence level increases?