14. Use the 'Salareis' data set that shows the first 5 observations as follows. index rank discipline phd service sex salary 1 Prof B 19 18 Male 139750 2 Prof B 20 16 Male 173200 3 AsstProf B 4 3 Male 79750 4 Prof B 5 Prof B 40 445 39 Male 115000 41 Male 141500 15. 1) Select female professors whose 'service' years is greater than 20 years 2) Sort the result of (1) in decreasing order by 'salary' 3) Calculate the average salary of the result of (1). Use 2 decimal places. 4) Calculate the average salary and standard deviation of professors' salaries by group of 'sex' and 'rank'