A 1.0m2 window consists of two sheets of glass (k=5.24 W/m.C) 5 mm thick separated by a space of insulation (k=0.026 w/m.C) 11 mm thick. . The room is maintained at 21C while the outside temperature is 8.0C. The heat transfer coefficients by air convection inside and outside the window are hint=10 w/m2.C and hext=40 w/m2.C.