A refinery produce three major products: gasoline, jet fuel and lubricants by distilling crude petroleum from two sources, Venezuela and Saudi Arabia. These two crudes have different chemical composition and therefore, provide different product mixes. From one barrel of Saudi crude, 0.25

barrel of gasoline, 0.45

barrel of jet fuel, and 0.2

barrel of lubricants are produced. Whereas, one barrel of Venezuelan crude produces 0.4

barrel of gasoline, 0.2

barrel of jet fuel, and 0.3

barrel of lubricants. The refinery losses 10 per cent of each barrel during the crude refining.

The crudes also differ in cost and availability: Up to 9,000 barrels per day of Saudi crude are available at the cost $\$ 20$ per barrel; Up to 6,000 barrels per day of Saudi crude are also available at the lower cost $\$ 15$ per barrel. The refinery has contracts with independent distributors to supply 2,000 barrels of gasoline per day, 1,500 barrels of jet fuel per day, and 500 barrels of lubricants per day. Formulate an optimization model in standard form to fulfill the requirements in the most efficient manner.