A manufacturer bonds a plastic coating to a metal surface. A random sample of nine observations on the thickness of this coating is taken from a week's output and the thickness (in millimeters) of these observations are shown below. Assuming normality, find a 90% confidence interval for the population variance. 19.8 21.7 18.7 20.1 21.6 19.7 19.8 20.7 20.8 Click the icon to view a table of lower critical values for the chi-square distribution. Click the icon to view a table of upper critical values for the chi-square distribution. Find the 90% confidence interval. < < (Round to four decimal places as needed.) 1/1 0/1 (0/