11-7. Historical data indicate that the standard deviation of a process is 6.3. A recent sample of size a. 28 produced a variance of 66.2. Test to determine if the variance has increased using a significance level of 0.05. b. 8 produced a variance of 9.02. Test to determine if the variance has decreased using a significance level of 0.025. Use the test statistic approach. c. 18 produced a variance of 62.9. Test to determine if the variance has changed using a significance level of 0.10.