0.5m thick plane wall has its two surfaces kept a 3000C and 2000C. Thermal conductivity of the wall varies linearly with temperature and its values at 3000C and 2000C are 25 W/mK and 15 W/mK, respectively. Then the steady heat flux through the wall is (IES-02)
(a) 8 kW/m2 (b) 6.33 W/m2K
(c) 20 W/m2K (d) 30 W/m2K