Evaluate ab whena 13 -2 6 and b4o a)233 2 6o b) 12 8 246 4-123 2 -6o c) 128 246 4 12o d) no solution

The answer is A) -23

A is a 1x3 Matrix while B is 3x1 Matrix. Since A has the same number of rows as that of the number of columns of B, they can be multiplied. A has 1 row and B has 1 column. So, their products is a 1x1 Matrix. 
Simply, the operation is:
(3)(-1) + (-2)(4) +(6)(-2) = -23