A horizontal 1.5-m-wide, 4.5-m-long double-pane window consists of two sheets of glass separated by a 3.5-cm gap

Question:

A horizontal 1.5-m-wide, 4.5-m-long double-pane window consists of two sheets of glass separated by a 3.5-cm gap filled with water. If the glass surface temperatures at the bottom and the top are measured to be 60ºC and 40ºC, respectively, the rate of heat transfer through the window is
(a) 27.6 kW

(b) 39.4 kW

(d) 66.4 kW

(e) 75.5 kW
(For water, use k = 0.644 W/m · K, Pr = 3.55, v = 0.554 × 10^-6 m²/s, β = 0.451 × 10^-3 K^-1. Also, the applicable correlation is Nu = 0.069Ra^1/3Pr^0.074).