In Order for a Matrix a to Have an Inverse $$A = \left( \begin{array} { c c } 3 & 6 \\- 2 & 1\end{array} \right)$$

In order for a matrix A to have an inverse, its determinant cannot be zero.Derive the
determinant of the following matrices: $$A = \left( \begin{array} { c c } 3 & 6 \\- 2 & 1\end{array} \right)$$
$$B = \left( \begin{array} { c c c } 1 & - 1 & 2 \\1 & 0 & 3 \\4 & 0 & 2\end{array} \right)$$
$\boldsymbol { X } ^ { \prime } \boldsymbol { X }$ where $X = \left( \begin{array} { l l } 1 & 10 \end{array} \right)$