Answer
See below
Work Step by Step
Given $\begin{bmatrix}
1 &0\\
3 & 1
\end{bmatrix}$
We can see that $A=A_{12}(3)$ corresponds to the matrix of a parallel to the y-axis.
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.