Volume of 1 Brick = (0.4 x 0.2 x 0.2) m = 0.016 m^3

Volume of long wall of length 6m, thickness 0.2m = (6 x 0.2 x 3) m = 3.6 m^3

Volume of short wall of length 4m, thickness 0.2m = (4 x 0.2 x 3) m = 2.4 m^3

Total Volume of Bricks = 6 m^3

Total Number of bricks = Total Volume of Bricks req. / Volume of 1 Brick = 6 / 0.016 = 375 Bricks