$($Data processing$)$ a$.$ You have collected information about cities in your state. You decide to store each city's name, population, and mayor in a file. Write a C$++$ program to accept data for a number of cities from the keyboard and store the data in a file in the order in which it'sentered. b$.$ Read the file created in Exercise $7$a$,$ sort the data alphabetically by city name, and display