adding subtracting and taking those difference in c++

C++ problem:

1. Enter the log in time in HH:MM:SS

2. Enter the log out time in HH:MM:SS

3. Calculate the difference in time and display it.

4. If the time difference is more then 8 hour, subtract 30 minutes from it.

5. If its 9 hour or more, subtract 45 minutes from it.

6. Display the actual end time.

I need help, to do this.