Chapter 2, problem 15 of Factory Physics by Hopp and Spearman. The reorder frequency is given, but there are no costs given for inventory, back order...

Chapter 2, problem 15 of Factory Physics by Hopp and Spearman. The reorder frequency is given, but there are no costs given for inventory, back order or stock out. If I use ONLY the information provided (assume that the costs are zeros), then the reorder quantity is fixed and independent of the order Quantity. Should I make assumptions on cost. What am I missing.