Recall that the addition between matrices is defined position by position, so this means, you take the element of a matrix and add it to the element of the other matrix that is located in the same position. For example
This necessarily means that to add two matrices, they MUST have the same dimension.
IN this case, we are adding a matrix of dimensions 2x4 with one with dimensions 2x3. Note that the second dimension does not coincide, so this operation can not be performed