P2) (25 pts.) The roof of a house consists of a 15-cm-thick concrete slab (k-2 W/m °C) that is 15 m wide and 20 m long. The convection heat transfer coefficients on the inner and outer surfaces of the roof are 5 and 10 W/m² °C, respectively. On a clear winter night, the ambient air is reported to be at 10°C while the night sky temperature is 235 K. The emissivity of the outer surface is -0.9. The house is maintained at a constant temperature of 20°C. Neglecting interior radiation heat transfer, determine the inner surface temperature of the roof and the heat lost in Watts. Hint: use a radiation heat transfer coefficient h,-3.50 W/m²-ºC. 15 m Taky-235 K T=10°C air Concrete roof =20°C Tin= 15 cm 20m