An aerospace company is developing a new fuel additive for commercial airliners. The additive is composed of three ingredients: X, Y, and Z. For peak performance, the total amount of additive must be at least 6 mL/L of fuel. For safety reasons, the sum of the highly flammable X and Y ingredients must not exceed 2.5 mL/L. In addition, the amount of the X ingredient must always be equal to or greater than the Y, and the Z must be greater than half the Y. If the cost per mL for the ingredients X, Y, and Z is 0.05, 0.025, and 0.15, respectively, determine the minimum cost mixture for each liter of fuel.