Davey and Carlie shared half a box of crackers. How many crackers did the box have when it was full?

Iadded davey’s charlie’s crackers because the problem says they each had 20 crackers. 20+20=40.But they only shared half a box of crackers then you have to add  the other half 40+40=80 crackers. So there are 80 crackers in the box.