At night, microscopic droplets of water falling through the atmosphere may freeze owing to radiative cooling even if the ambient air temperature is above freezing. For very fine droplets of radius a, the convective heat transfer coefficient is inversely proportional to size, say given by h = 1.3 k/a, where k is a constant. If a certain size droplet freezes at air temperature of 3 C, what air temperature would be required for a droplet half as big? You may assume the droplets "see" only the night sky. Also assume that the heat transfer by the combined mechanism of convection and radiation has reached steady state. At the freezing condition, the droplet surface temperature is 0 C