Answer
$4$
Work Step by Step
$A=\left[ \begin{matrix}
1 & 0 & 2 & 1 \\
0 & 1 & -1 & 2 \\
4 & 2 & 1 & 0 \\
0 & 0 & 5 & 1 \\
\end{matrix}
\right] $
To find the trace of a matrix calculate the sum of the main diagonal
entries.
$Tr(A)=1+1+1+1=4$
