The composite wall of an oven consists of three materials, two of which are of known thermal conductivity, kA = 30 W/m·K and kC = 60 W/m·K, and known thickness, LA = 0.3 m and LC = 0.25 m, respectively. The third material, B, which is sandwiched between materials A and C, is of known thickness, LB = 0.25 m, but unknown thermal conductivity kB. Under steady-state operating conditions, measurements reveal an outer surface temperature (on outer surface of material C) of Ts, o = 20◦C, an inner surface temperature (on inner surface of material A) of Ts, i = 400◦C, and an oven temperature of T[infinity] = 600◦C. The inside convection coefficient h = 20 W/m2 ·K. (a) What is the value of kB? (b) Sketch the temperature distribution. (c) Calculate the overall heat transfer coefficient.