Question: Incredible Indelible Ink Company mixes three additives, A1, A2, and A3, in different proportions, and a base to obtain different colors of ink. Red ink is obtained by mixing A1, A2, and A3 in the ratio of 3:1:2, blue ink in the ratio of 2:3:4, and green in the ratio of 1:2:3. After these additives are mixed to make a certain color, an equal amount of base is added to finish making this color. The company currently has 1000 gallons of A1, 1500 gallons of A2, 2000 gallons of A3, and 4000 gallons of base. Given that the selling price per gallon for each type of ink is the same, formulate an LP model to determine how these resources should be used to obtain the maximum revenue. (12 points)