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 = 65 W/m·K, and known thickness, LA = 0.35 m and LC = 0.25 m. 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 = 22◦C, an inner surface temperature (on inner surface of material A) of Ts,i = 600◦C, and an oven temperature of T[infinity] = 800◦C. If the inside convection coefficient h = 25 W/m2 ·K, what is the value of kB?