Interesting question.  I don’t know Secondary 3 math, but logically this is how I see it.

a. A divisible positive integer of 385 is 7, giving 55.  So the cuboid would comprise of an area of 55 blocks of height 7 blocks.  Factorising 55 gives 5 and 11.

Hence the dimensions of the cuboid are 5 cm, 11 cm and 7cm.

b. The cube root of 385 is approximately 7.xxx.  Hence the smallest cube that can be formed is 7cm cube, using up a total of 7x7x7 = 343 cubes.  So the total remaining cubes = 385-343 = 42.

(a)

Since all 385 were used to form the cuboid,

find the factors of 385.

The first factor that comes to mind is 5.

385 / 5 = 77

Hence, the other 2 factors are 7 and 11.

Dimension of the cuboid -> 5cm by 7cm by 11cm

(b)

Cube root of 385 -> 7.27….

The largest cube that can be formed is 7 x 7 x 7 = 343 cubes

Left over -> 385 – 343 = 42 cubes