Answer
Invertible
Work Step by Step
The matrix is non-invertible if and only if $D=0$.
Upper A$=\begin{bmatrix}
1 & 0 &2&-1\\
0 & 1 &2 &4\\
0 & 0 & -1 &15\\
0 & 0 & 0& 133
\end{bmatrix}$
Hence here $D=-1.1.1.(-1).133=133\ne 0$, thus the matrix is invertible.