Why do this problem?
is extremely open and invites exploration at whatever the level of pupils' understanding. It can lead to a pupil having a wider understanding of what it is to multiply. Many opportunities are built in for exploring number patterns.
I have found it good to lay out some counters or cubes in the initial pattern and invite pupils to talk about what they notice, with the simple prompt, "Tell me what you see!".
What do you notice?
Can you describe what you see for everyone so that they might see it too?
When appropriate - How did you work that out? What adding did you actually do?
Get the pupils to imagine that the pattern you've presented to them at the start is just one item in a sequence. Ask them to create/talk about what the previous/next ones might be.
For the Most Able
When this activity has satisfied the pupil then go to 3D Stacks
for a much larger 3D exploration giving numbers that have very many properties and relationships.
Joining in with pupils so that they are very involved with the talk would be a big asset for many children.