The horizontal roof of a building is coated with black tar. The roof is well-insulateed underneath, while the upper surface is exposed to ambient air at 300K through a convective heat transfer coefficient of 5 W/m^2*k. Calculate the roof temperature for the following condittions. a. a clear sunny day with incident solar radiation flux of 600 W/m^2 and an effective ambient sky temperature of 40K. b. a clear night with an effective ambient sky temperature of 40K.