Work time registration problem

Hello!

I try to make a program that calculates my starting, ending and total workhour time. You can see my attachments. The first is when do I start at work. The next (slutt) is when I finish at work, and then it's pauses and total worked hours.
But I want to make a program where I can punch whatever I want, and then Excel give me the answer on the last time.

For example: If I want to work 12 hours one day, and I need 00:45 (45 minutes) brake (pause), and I need to leave 20:00, then Excel will give me the time I need to start at work in the A2. In this case 07:15.

Other example: I want to start 07:30, and I need to work 14 hours with 1 hour pause, then the end-time should give me 22:30.


Hope you understand what I mean. Is this possible with only using A2, B2, C2 and D2? Or do I need some help-calculating other places?

Thanks!