The volume of a wall, 5 times as high as it is broad and 8 times as long as it is high, is 128 m3.

Note : It should be 128 m3 instead of 12.8 m3

(b) 40 cm
Let the breadth of the wall be x cm.
Then, its height = 5x cm

and its length $=(8 \times 5 x) \mathrm{cm}$

 = 40x cm

Hence, the volume of the wall $=(40 x \times x \times 5 x) \mathrm{cm}^{3}$

It is given that the volume of the wall = 128 m3.
Therefore,

$\Rightarrow 40 x \times x \times 5 x=128 \times 100 \times 100 \times 100$

$\Rightarrow 200 x^{3}=128000000$

$\Rightarrow x^{3}=640000$

$\Rightarrow x^{3}=(40 \times 40 \times 40)$

$\Rightarrow x=40 \mathrm{~cm}$