Formula help

Please could some one help me out? Iv worked out how to do the formulas for both totalling the check mark and the number of adults or children. But what I really want is to be able to have have for mail a that adds up the number of ‘checked’ adults coming to the party as well as the number of checked children. Whilst all I’m getting in the red exclamation mark, or just the total of ‘checked’ people added onto the number or adults or children. If that makes sense. 🙈