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

Essay

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