I know the third one is undefined for both because it isn't invertible, but I'm not sure how to do A and B.Aj is (1 ;4) and Ai is (3;-1).

Explaination/ help is appreciated!

\(\mathbf{A}^{-1} \begin{pmatrix} 3 \\ 1 \end{pmatrix} = \begin{pmatrix} 2 \\ 1 \end{pmatrix}\)

\(\mathbf{B}^{-1} \begin{pmatrix} 3 \\ 1 \end{pmatrix} = \begin{pmatrix} -1 \\ 4 \end{pmatrix}\)