Heat And Thermodynamics

A composite slab consists of two materials having coefficient of thermal conductivity \(\mathrm{K}\) and \(2 \mathrm{~K}\), thickness \(\mathrm{x}\) and \(4 \mathrm{x}\) respectively. The temperature of the two outer surfaces of a composite slab are \(\mathrm{T}_2\) and \(\mathrm{T}_1\left(\mathrm{~T}_2 > \mathrm{T}_1\right)\). The rate of heat transfer through the slab in a steady state is \(\left[\frac{\mathrm{A}\left(\mathrm{T}_2-\mathrm{T}_1\right) \mathrm{K}}{\mathrm{x}}\right] \cdot \mathrm{f}\) where '\(\mathrm{f}\)' is equal to