A dormitory at a large university, built 50 years ago, has exterior walls constructed of L_s = 25-mm-thick sheathing with a thermal conductivity of k_s = 0.1 W/m · K. To reduce heat losses in the winter, the university decides to encapsulate the entire dormitory by applying an L_i = 25-mm-thick layer of extruded insulation characterized by k_i = 0.029 W/m · K to the exterior of the original sheathing. The extruded insulation is, in turn, covered with an L_g = 5-mm-thick architectural glass with k_g = 1.4 W/m · K. Determine the heat flux through the original and retrofitted walls when the interior and exterior air temperatures are T_∞,i  = 22°C and T_∞,o = –20°C, respectively. The inner and outer convection heat transfer coefficients are h_i = 5 W/m²  · K and h_o = 25 W/m²  · K, respectively.