First of all, what is meant by a numerical matrix?

Is it a matrix whose ij entries are not 0?

Is it a matrix whose ij entries have at least 1 number?

What are 2 numerical, 3x3, matrices A, B that multiply to the 0 matrix and A and B are not zero matrices themselves.

I have a simple solution to this depending on the definition of a numerical matrix. If it is the first definition then I need an example.

Also, how do I find a 3x3 matrix B such that for every 3x3 matrix A, AB = 3B?

I don't think it's possible, what if A is a zero matrix?