This activity may be used as a follow-on for those who have successfully worked at Doplication.
Let me help you visualise this representation of a 3D situation.
It's kind of two sets of three adjacent cubes with balls at each vertex. Then there is a ball in the centre of each cube.
Towards the bottom left of the picture are the eight large balls, then going backwards there are eight medium red balls and further back are eight small ones.
In the centre of the front three cubes are three orange balls and at the centre of the rear cubes are three brown ones.