A vertical 0.9-m-high and 1.8-m-wide double-pane window consists of two sheets of glass separated by a 2.2-cm

Question:

A vertical 0.9-m-high and 1.8-m-wide double-pane window consists of two sheets of glass separated by a 2.2-cm air gap at atmospheric pressure. If the glass surface temperatures across the air gap are measured to be 20°C and 30°C, the rate of heat transfer through the window is
(a) 19.8 W

(b) 26.1 W

(d) 34.7 W

(e) 55.0 W

(For air, use k = 0.02551 W/m · K, Pr = 0.7296, v = 1.562 × 10^-5 m²/s. Also, the applicable correlation is Nu = 0.42Ra^1/4 Pr^0.012 (H/L)^-0.3)
(For air, use k = 0.02588 W/m · K, Pr = 0.7282, v = 1.608 × 10^-5 m²/s)