6. Write a C program using system I/O calls to 7. a) open an existing text file passed to your program as a command line argument, then b) display the content of the file, c) ask the user what information he/she wants to append d) receive the info from the user via keyboard e) append the info received in d) to the end of the file f) display the updated content of the file. Redo question 6 above but this time uses standard I/O calls.