The linear transformation $\ltdefn{R}{M_{12}}{M_{21}}$ is invertible. Determine a formula for the inverse linear transformation $\ltdefn{\ltinverse{R}}{M_{21}}{M_{12}}$. \begin{equation*} \lt{R}{\begin{bmatrix}a & b\end{bmatrix}} = \begin{bmatrix} a+3b\\ 4a+11b \end{bmatrix} \end{equation*}