Answer
Invertible
Work Step by Step
The matrix is non-invertible if and only if $D=0$.
Upper A$=\begin{bmatrix}
1 & 1 &1&1\\
0 & 2 & 0 &2\\
0 & 0 & -2 & -2\\
0 & 0 & 0& -4
\end{bmatrix}$
Hence here $D=1.2.(-2).(-2)=8\ne 0$, thus the matrix is invertible.