A steady fire with an energy release rate of 500 kW occurs in a room 3m wide, 3m long, and 2.4 m high, with a door opening which is 1.8 m high and 0.6m wide. the ambient temperature is 20 degree celcius. Calculate the average gas temperature in the upper layre of the room after 60 seconds and 600 seconds if: (a): the construction is made of lightweight concrete with wall thickness 0.15 m (b) the construction is made of double gypsum plaster board, each plate 0.012 m thick? (c) as in (b), but insulated with mneral wool of thickness 0.05m, with k=0.041 W/(mK), p=100 kg/m^3, and c=800 J/(kgK)