What am I doing wrong when trying to find a determinant of this 4x4 I have to find the determinant of this 4x4 matrix:
$
\begin{bmatrix}
 5 & -7 & 2 & 2 \\
 0 & 3 & 0 & -4 \\
 -5 & -8 & 0 & 3 \\
 0 & -5 & 0 & -6 \\
\end{bmatrix}
$

Here is my working which seems wrong according to the solutions. What am i doing wrong?:



And here is the solution:


Your $3\times3$ determinant has to have a $-(-5)$ in the front. Hope you can see that from the formula of a determinant for a $3\times 3$ matrix.
