Heat is transferred steadily through a 0.2-m thick 8 m X 4 m wall at a rate

Question:

Heat is transferred steadily through a 0.2-m thick 8 m X 4 m wall at a rate of 1.6 kW. The inner and outer surface temperatures of the wall are measured to be 15°C to 5°C. The average thermal conductivity of the wall is
(a) 0.001 W/m • °C
(b) 0.5 W/m • °C
(c) 1.0 W/m • °C
(d) 2.0 W/m • °C
(e) 5.0 W/m • °C