2. (4 points). The composite wall of an oven consists of three materials, two of which are of known thermal conductivity, kA = 20 W/(mK) and kc = 50 W/(mK), and known thickness,LA = 0.30 m and Lc = 0.15 m. The third material, B, which is sandwiched between materials A and C, is of known thickness, LB = 0.15 m, but unknown thermal conductivity kB. Under steady-state operating conditions, measurements reveal an outer surface temperature of Ts,o=20°C, an inner surface temperature of Tsi = 600°C, and an oven air temperature of T infinity=800°C.The inside convection coefficient h is known to be 25 W/m² - K. What is the value of kB?