Heat is lost steadily through a 0.5-cm thick 2 m × 3 m window glass whose thermal conductivity is 0.7 W/m · K. The inner and outer surface temperatures of the glass are measured to be 12°C to 9°C. The rate of heat loss by conduction through the glass is
(a) 420 W

(b) 5040 W

(c) 17,600 W

(d) 1256 W

(e) 2520 W