Let length, breadth and height of solid brick be x units, 2x units and 3x units. Volume = Number of brick ‌‌‌‌‌‌‌‌‌‌‌=L×B×H4 ‌‌‌‌‌‌‌‌‌‌‌=x×2x×3x ‌‌‌‌‌‌‌‌‌‌‌=6x2 Now let x=1,6×(1)3=6 at x = 2, 6×(2)3=48 at x = 3, 6×(3)3=222 at x = 4, 6×(4)3=384 at x = 5, 6×(5)3=750 Hence, at x = 5, number of cubes are going above 400.