Three beachcombers collect shells and other items from the beach each morning to sell in...

Three beachcombers collect shells and other items from the beach each morning to sell in their shops. They decide to divide the beach into three pieces so that each hunts in her own area. The beach they collect from is made up of 600 linear feet of sandy beach, 600 linear feet of rocky beach, and 600 linear feet of grassy beach. The preferences of each beachcomber are given in the following table, where larger numbers indicate a greater preference.

If Sondra is the first divider and Elsa is the first chooser, find a proportional, envy-free division of the beach among the beachcombers.