Answer 1

40 cm
Let the breadth of the wall be x cm.
Then, its height = 5x cm
and its length = (8 × 5x)
                   = 40 × cm
Hence, the volume of the wall = (40x × x × 5x) cm³
It is given that the volume of the wall = 128 m³.
Therefore,

⇒ 40x × x × 5x  = 128 × 100 × 100 × 100

⇒ 200x³  = 128000000

⇒ x³ = 640000

⇒ x³ = (40 × 40 × 40)

⇒ x = 40 cm