d
$\Delta=\left|\begin{array}{ccc}- k & 3 & -14 \\ -15 & 4 & - k \\ -4 & 1 & 3\end{array}\right|=121- k ^{2}$
$\Delta \neq 0 \quad k \in R -\{11,-11\} \quad$ (Unique sol.)
If $k =11$
$\Delta_{2}=\left|\begin{array}{ccc}-11 & 3 & 25 \\ -15 & 4 & 3 \\ -4 & 1 & 4\end{array}\right| \neq 0$
$No \,solution $
If $k =-11$
$\Delta_{z}=\left|\begin{array}{ccc}11 & 3 & 25 \\ -15 & 4 & 3 \\ -4 & 1 & 4\end{array}\right| \neq 0$
$No \, solution $