Please help me quickly!!

ASD Flight School has three contractor spare parts manufacturing company in Europe: ABC Company supplies Q family of spare parts, XYZ Company supplies Z family of spare parts and PRS Company supplies W family of spare parts. The monthly demand for Qs is 2000 units, for Zs is 10000 whereas that for Ws is 50000. Qs cost the company $1000, Zs cost $500, and Ws cost $200 and the company has a holding cost of 10 percent. Now, ASD Flight School has to place separate orders with ABC, XYZ, and PRS and receive separate shipments. The fixed cost of each shipment is $20,000. In the case of combining orders $1000 of cost is added to the fixed cost for each

a. What is the optimal order size and order frequency with each of the companies?

b. The company thinks of combining all parts with the same contract manufacturer. This will allow for a single shipment of all products from Europe. What is the optimal order frequency and order size from the combined orders?

c. What is the optimal order frequency and order size form a tailored aggregation?

d. How much reduction in cycle inventory can the company expect as a result of these alternatives?