Ford and GM carry spare parts for their dealers at a third-party warehouse in the GTA area. Demand for Ford spare parts is 150 units per month, whereas demand for GM parts is 200 per month. Each spare part costs $100, and the holding cost is 25% for Ford and 20% for GM. Currently each company uses a separate truck to ship these parts. Each truck has a fixed cost of $500 for Ford and $450 for GM.

1. What is the optimal order quantity for Ford?
2. What is the optimal order quantity for GM?
3. What is the total annual cost of both companies combined?
4. A third-party provider has offered to combine shipments for each of the two companies one a single truck. This will increase the cost of each truck to $640. If the two companies agree on the joint shipment, what is the optimal lot size for Ford?
5. What is the optimal lot size for GM?
6. What is the total annual cost for both companies combined when shipping jointly?