The composite wall of an oven consists of three materials, two of which are of known thermal conductivity, kA = 25 W/m ⋅ K and kC = 60 W/m ⋅ K, and known thickness, LA = 0.40 m and LC = 0.20 m. The third material, B, which is sandwiched between materials A and C, is of known thickness, LB = 0.20 m, but unknown thermal conductivity kB. Under steady-state operating conditions, measurementsreveal an outer surface temperature of Ts, o =20ºC, an inner surface temperature of Ts, i= 600ºC, and an oven air temperature ofT¥=800ºC. The inside convection coefficienth is known to be 25 W/(m^2•K). What isthe value of kB?