Time Remaining?

[Exc3ln00b]

I am stuck - I have a running hours time sheet or hours worked. Total hours should be 40. How can I get an hours remaining formula based on this?

Edit- have total hours, required
Hours.

I want the remaining time to change as hours are calculated.

 

[Exc3ln00b]

Total hours (b10) is based on sum of times in a2-a7. I want remaining hours to be subtracted from 40 hours - total hours presently.

hope I make sense