In your example, and given a choice, I would prefer to use "in" which suggests to me that "78" is part of the complete number. "With" would, for me, suggest the possibility that "78" is separate from the main number, as in "123 78_ or "123-78".
In your example, and given a choice, I would prefer to use "in" which suggests to me that "78" is part of the complete number. "With" would, for me, suggest the possibility that "78" is separate from the main number, as in "123 78_ or "123-78".