A+C+E Sum

This is a pretty small point in terms of the entire explanation, but technically, shouldn't the greatest possible sum of A, C, and E be 9, if all three of them were 3? In the end, it doesn't really affect the solution that much, but I did want to ask if there was something I was missing. If I'm misunderstanding this problem can someone please provide an explanation?

@strategicporpoise same question lol