This lecture covers the study of conductive heat transfer in a composite wall, analyzing the distribution of temperatures, determining surface temperatures, and solving the problem using the first law of thermodynamics. The demonstration includes the parabolic distribution in material A, temperature at contact points, and linear distribution in material B. The determination of temperatures To and T₂ is explained through numerical applications and the use of thermal resistance concepts. Conclusions are drawn based on the calculated temperatures, providing insights into the thermal behavior of composite walls.