Excel formula with Morning in and out and afternoon in and out

Hi there!

I just wanted to ask if anyone can help me create a formula to compute for hours at work with multiple time ins and outs. Our lunch break in our small office is very relative. We can either spend a lot or less time during lunch break as long as we were able to complete an 8 hour/ day routine.

Ex:
time in(am) Time out (pm) Time in (pm) Time out (pm)
2-28-13 10:00am 12:30nn 1:00pm 7:00pm

Anyone who can help will be such heroes! Thanks!