A masonary wall (k = 0.75 W/m-K) transfers 80% of the heat loss through another wall (k = 0.25 W/m-K, x = 100 mm). If the temperature difference across both the walls is same, the thickness of masonary wall would be (a) 150 mm (c) 300 mm (b) 240 mm (d) 375 mm