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This sequent is provable.
\begin{logicproof}{1}
\lnot \lnot k \imp (l \land m) & \prem \\
\lnot \lnot \lnot l \imp m & \prem \\
m \lor \lnot m & $\LEM$ \\
\begin{subproof}
m & \assum \\
\lnot \lnot m & $\lnot \negi 4$ \\
l \lor \lnot \lnot m & $\ori{2} 5$ \\
\lnot k \lor (l \lor \lnot \lnot m) & $\ori{2} 6$
\end{subproof}
\begin{subproof}
\lnot m & \assum \\
\lnot \lnot \lnot \lnot l & $\MT 2,8$ \\
\lnot \lnot l & $\negnege 9$ \\
l & $\negnege 10$ \\
l \lor \lnot \lnot m & $\ori{1} 11$ \\
\lnot k \lor (l \lor \lnot \lnot m) & $\ori{2} 12$
\end{subproof}
\lnot k \lor (l \lor \lnot \lnot m) & $\ore 3, 4-7, 8-13$
\end{logicproof}