A double-pane window of surface area \(A\) consists of two outer glass panes, each of thickness \(d\) and thermal conductivity \(k_g\), enclosing a layer of stagnant air also of thickness \(d\) and thermal conductivity \(k_a\). The inner and outer faces of the window assembly are maintained at constant temperatures such that the total temperature difference across the entire assembly is \(\Delta T\). Assuming steady-state heat conduction perpendicular to the panes, which of the following expressions correctly gives the rate of heat transfer \(H = \dfrac{Q}{\Delta t}\) through the window?