A union spokesman complained to company A that labourers employed there were paid lower wages on average than those employed by company B. A randomly chosen sample of 60 labourers from company A...

A union spokesman complained to company A that labourers employed there were paid lower wages on average than those employed by company B. A randomly chosen sample of 60 labourers from company A yielded a weekly average of $556.6 and a weekly standard deviation of $10.56.
A random sample of 60 labourers employed by company B yielded a weekly sample mean and standard deviation of $561.44 and $19.36, respectively.
a. What estimator would you use to generate a point estimate for difference in the average weekly wage paid out between company A and company B? State and describe two properties you would like the estimator to possess?
b. Approximate the 95% confidence interval for the difference in the average weekly wage between company A and company B.