A certain double-pane window consists of two glass sheet, each 80 cm x 80 cm x 0.30 cm, separated by a 0.30 cm stagnant air space. The indoor surface temperature is 20 deg C, while the outdoor surface temperature is 0 deg C. How much heat passes through the window each second? k= 2 x 10^-3 cal/s cm C for glass and 2 x 10^-4 cal/s cm C for air.