What 3x2 matrix could be added to a second 3x2 matrix without changing that second matrix?

The 3x2 matrix that has all its elements zero.

A zero matrix is one which has all its elements zero. Here is a 3x3 zero matrix:

The name of a zero matrix is a bold-face zero: **0**,
although sometimes people forget to
make it bold face.
Here is an interesting problem:

Form the above sum. No electronic calculators allowed!