Let A be a $2 \times 2$ matrix and $I$ be the $2 \times 2$ identity matrix such that
$$A ^ { 2 } = \left[ \begin{array} { l l }
2 & 1 \\
1 & 5
\end{array} \right]$$
What is the value of the determinant $| ( \mathbf { A } - \mathbf { I } ) ( \mathbf { A } + \mathbf { I } ) |$?\\
A) 2\\
B) 3\\
C) 4\\
D) 5\\
E) 6