6. A corporation is interested in estimating the total earnings from sales of colour television sets at the end of a 3-month period. The total earnings figures are available for all districts within the corporation for the corresponding 3-month period ofthe previous year. Asimple random sample of 13 district offices is selected from the 123 offices within the corporation. (a) Estimate the current mean earnings ,uy using the 1) ordinary method or 2) ratio estimation that based on the sample. Place a bound on the error of estimation with 95% confidence level. (b) Use a ratio estimator to estimate Ty , and place a bound on the error of estimation with 95% confidence level. Use the data in the table and take Tx = 128,200. (c) Use a regression estimator to estimate the mean earnings ,uy , and place a bound on the error of estimation with 95% confidence level. Compare your answer with that in part (a). Are there any advantages in using the regression estimator