2. A large concrete wall 50 cm thick is initially at 60 C. One side of the wall is insulated. The other side is suddenly exposed to combustion gases at 900 C with a heat transfer coefficient of h= 25 W/m²K. Determine: a. How long it would take for the insulated surface to reach 600 C. b. The heat transferred to the wall per square meter of surface area during this time. Use the following properties: K= 1.2 W/m.K; C,-840 J/kg.K; p=500 kg/m³; a=0.3 X 10-5 m²/s. (Hint: An insulated wall may be considered as 1/2 of the wall that is exposed to gases on both sides).