The Lauren Shur Tub Company manufactures two lines of bathtubs, called model A and model B. Every tub requires blending a certain amount of steel and zinc; the company has available a total of 25,000 lb of steel and 6,000 lb of zinc. Each model A bathtub requires a mixture of 125 lb of steel and 20 lb of zinc, and each yields a profit of $90. Each model B tub requires 100 lb of steel and 30 lb of zinc and can be sold for a profit of $70. Find by graphical linear programming the best production mix of bathtubs.