Boy, it's hard to see columns in your matrices. One way to line things up by using a fixed-width font is to wrap a matrix or table in the CODE tags (the icon # above the editor).
I assume the matrices are as follows.
I also assume that when the stores receive their shipments, the orders are added to their corresponding stock. I don't see the need for multiplication. Can you figure the answer?Code:Item1 Item2 S = StoreA 8 15 StoreB 20 17 Item1 Item2 O = StoreA 2 1 StoreB 12 0