A layer of 5 cm thick insulating brick having conductivity of 1.5 W/m K is placed between
two 0.5 cm thick steel plates. The conductivity of mild steel is 50 W/m K. The faces of brick
adjacent to the plates are rough having solid-to-solid contact of 30% of the total area. The
average height of the asperities is 0.1 cm. if the outer plate surface temperatures are 100°C
and 500°C respectively, calculate the rate of heat transfer per unit area. The conductivity of
air is 0.02 W/m K.

i am getting a wrong answer plz help me with the concept here