15. Find the g-inverse of the symmetric matrix A where

$$

A = \begin{bmatrix}

3 & 1 & 0 & 1 \\

1 & 4 & -1 & 2 \\

0 & -1 & 6 & 2 \\

1 & 2 & 2 & 4

\end{bmatrix}

$$