The outer diameter, d, of a cylinder is processed on an automatic machine with upper and lower tolerance limits of d + t_U and d − t_L. The production process follows a normal distribution with mean μ and standard deviation σ. Oversized cylinders are reworked at the cost of c₁ dollars each. Undersized cylinders are salvaged at the cost of c₂ dollars each. Develop the decision tree, and determine the optimal setting d for the machine.