If A is matrix and B is matrix such that A'B and BA' are both defined, then B is of the type.
Given that matrix A is 3 x 4.
Let the B matrix be P x Q.
Therefore, A' is 4 x 3.
Since A'B is defined, so number of columns of A' must be equal to number of rows of B, therefore, P = 3.
Also, BA' is defined, so the number of columns of B must be equal to number of rows of A', then Q = 4.
Therefore, matrix B is 3 x 4.