Matrix multiplication

For the following pairs of matrices determine whether matrix multiplication is valid for A x B and B x A, and for the valid cases indicate the dimension of the resulting matrix. 1 2 1 4 5 6 2 A: 2 1 2 ;B: 6 5 4 1 2 1 3 A: 2 1 \"B: 1 1 3 1 3 2 1 2 1 1 1 4 A : 2 1 2 , B: ( ) 3 2 1 2 1 1 1 1 10 5 A: 4 ; B: 3 2 0 2 0 1 7 4 8 6 A: (1 2 9), B: 5 2