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?