The discussion focuses on the application of the lever rule in phase diagrams, specifically regarding a eutectic composition of 50% To and 50% Lb. When cooling this homogeneous liquid to room temperature, it separates into two distinct phases: alpha and beta. The lever rule is used to determine the relative concentrations of these phases. For the beta phase, the concentration is calculated using the formula: (Lb(eutectic) - Lb(alpha)) / (Lb(beta) - Lb(alpha)). Conversely, the alpha phase concentration is determined by: (Lb(beta) - Lb(eutectic)) / (Lb(beta) - Lb(alpha)). This method illustrates that the relative concentration of each phase can be understood through the length ratios of specific lines on the phase diagram, highlighting the relationship between the phases at the eutectic point.