A random sample of professional wrestlers was obtained, and the annual salary (in dollars) for each was recorded. The summary statistics were x 5 47,500 and n 5 18. Assume the distribution of annual salary is normal with s 5 8,500. a. Find a 90% confidence interval for the true mean annual salary for all professional wrestlers. b. How large a sample is necessary for the bound on the error of estimation to be 3000? c. How large a sample is necessary for the bound on the error of estimation to be 1000?