For matrix subtraction to be defined, both the matrices involved in the subtraction must be of the same size and order.
This means,
The number of rows and columns of the first matrix must be equal to the number of rows and columns of the second matrix.
Matrix A has 3 rows and 2 columns.
Matrix C has 2 rows and 2 columns.
Since both their orders aren't equal, they can't be subtracted.
