Let us presume that a product is made at two of our factories which we wish to ship to three of our warehouses. We produce 18 at factory A and 22 at factory B; we want 10 in warehouse 1, 20 in warehouse 2, and 10 in warehouse 3. Per unit transportation costs are A to 1, $4; A to 2, $2; A to 3, $3; B to 1, $3; B to 2, $2; B to 3, $1.