A shop window pane of thickness d = 0.5 cm and area A = 10 m^2 has the thermal conductivity λ = 0.76 W/mK. The two heat transfer coefficients for inside and outside are each α = 10 W/m^2K. ϑ20 = 20 °C was measured for the interior temperature of the room. Examine the temperature gradient across the disc. Below what outside temperature ϑa do ice flowers form on the inside of the shop window? Enter your result in degrees Celsius and to one decimal place.