Approximate the heat transfer rate through a 0.8-m by 2-m double-pane window if a convective layer on

Question:

Approximate the heat transfer rate through a 0.8-m by 2-m double-pane window if a convective layer on a vertical pane of glass can be approximated as having an R-factor of 1 m2∙°C/W. The resistivity of the air layer between the panes can be approximated as R = 0.4 m2∙°C/W. The temperature difference across the window is 30°C.
(A) 60 J/s
(B) 40 J/s
(C) 20 J/s
(D) 10 J/s