A 3 m diameter spherical tank holds liquid nitrogen at 1 atm and −196 °C; ambient 15 °C; combined h = 35 W/m^{2}·°C; 5 cm fibreglass insulation, k = 0.035 W/m·°C; h_{fg} = 198 kJ/kg, ρ = 810 kg/m^{3}. Determine (a) the rate of heat gain (answer in W) and (b) the rate of evaporation of nitrogen (answer in kg/s).