Basically create points for stores and warehouses. Use the find nearest tool to get the nearest warehouse to the store, Then its simple enough to join the items data set to the stores and then sum up the distances traveled per item. The only issue was I did not know why we had to multiply the distance by assigned. That did not make sense to me but to match the numbers in the solution, I had to do that. I'm guessing something to do with the previous solution. I love spatial problems but wish I had the drivetime data set.