Thabiso places 6 cylinders on the three cuboids as shown. The first row of cylinders leaves an equal distance of 4.5 cm on either side. Find the diameter of each cylinder.

From the previous problem, the length of each cuboid is $l = 9$ cm.
When three cuboids are placed side-by-side along their length, the total length of the base is $3l$.
Total length of base $= 3 \times 9 \text{ cm} = 27 \text{ cm}$.

The first row has 3 cylinders. Let $D$ be the diameter of each cylinder.
The total length occupied by the 3 cylinders is $3D$.
There is an equal distance of 4.5 cm on either side of the first row of cylinders.
So, the total length of the base is the sum of the two gaps and the total diameter of the three cylinders.

Combine the constant terms:

Subtract 9 from both sides:

Divide by 3:

The diameter of each cylinder is $\text{6 cm}$.