Discrete Math

You are observing Grace, the former 203 GSI, giving two IAs a logical test to prepare them for the upcoming semester. The conversation proceeds as follows: " Grace: I am giving you each a slip of paper with a non-negative integer on it. Abigail looks down at her paper and sees 6. Emma looks down at her paper and sees 4. Grace tells them that their numbers sum to either 8 or 10, but does not tell them which. It is Abigail and Emma's job to figure out whether their numbers sum to 8, or whether they sum to 10, without looking at each other's papers. Grace asks each of them, alternating back and forth, starting with Abigail, if the sum of the numbers is 8 or if the sum of the numbers is 10. They can either pass, or guess. If either guess correctly, they succeed; otherwise, they fail. Will either of them be able to guess the answer with certainty? Justify answers in either case