Let A be a 2 X 2 matrix, B a 2 X 2 matrix, C a 2 X 3 matrix, D a 3 X 2 matrix, and E a 3 X 4 matrix. Determine which of the following matrix expressions exist and give the sizes of the resulting matrices when they do exist. (If an answer does not exist, enter DNE.) (a) AB :X: (b) (ABC 7X7 (9) 3(XCD) + (4A>(BC)D X