Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 6 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 98? Show your work and explain how you arrived at your answers. There are sample student explanations in the feedback to questions 1, 3, 5, 9, 11, and 20 that show the level of detail that is expected in your explanations.