calculate time start and finish times and deducts breaks

Hi all this might seem like a long shot but what I want. I have got my work time sheet which I fill in daily as i am a lorry driver. but I would like is to be able to fill this in on my phone daily and it calculate my work time for me.

So if I put in my start time and FINISH time it calculates my total duty plus after I have input my break time and POA Time it add these two up and deducts this from my total duty and in puts it in to the working time.

Can any one help I hope this make sense.

Try
I5=D5-C5
J5=I5-(F5+G5)

You didn't specify driving time...