A composite wall having three layers of thickness 0.3 m, 0.2 m and 0.1 m and of thermal conductivities 0.6, 0.4 and 0.1 W/ mK, respectively, is having surface area 1m2. If the inner and outer temperatures of the composite wall are 1840 K and 340 K, respectively, what is the rate of heat transfer? (IES-07)
a. 150 W b. 1500 W
c. 75 W d. 750 W