The hot surface of a circuit board is steadily dissipating heat at 8 w to the ambient air of 20 °c. the board itself is 15 cm wide and 20 cm long, and the heat loss on the other side of the board can be neglected. determine the average temperature of the hot surface when (a) the board is placed vertically (along 20-cm side), (b) the board is placed horizontally with the hot surface facing up, and (c) the board is placed horizontally with the hot surface facing down. assume the board surface has an emissivity of 0.8 and the surrounding surfaces are at 20 °c.