12. (12 points) Fill the 16 cells in the table with the numbers $1, 2, 3, \cdots, 15, 16$, and satisfy the following conditions.
\begin{tabular}{|c|c|c|c|}
\hline$A$ & $B$ & $C$ & $D$ \\
\hline$E$ & $F$ & $G$ & $H$ \\
\hline$J$ & $K$ & $L$ & $M$ \\
\hline$N$ & $P$ & $Q$ & $R$ \\
\hline
\end{tabular}
(1) $A+C+F=10$;
(2) $B+H=R$;
(3) $D-C=13$;
(4) $E \times M=126$;
(5) $F+G=21$;
(7) $G \div J=2$;
(7) $H \times M=36$;
(8) $J \times P=80$;
(9) $K-N=Q$. Then $L=$ $\qquad$
【Solution】Solution: From (8) we know: $J \times P=80=5 \times 16=10 \times 8$,
From (7) $G \div J=2$ we know, $J$ could be 5 or 8,
Let's assume $J=5$, then from (7) we know, $G=10$, from (5) we know, $F=11$ which contradicts (1), $\therefore J=8, P=10, G=16, F=5$, from the remaining numbers, combining (2) $B+H=R$, we know, $B=8, R=11$, then combining (1) and (3), we know, $A+C=5$, leading to $A=3, C=2, D=15$, combining (9) we know, $K=13, N$ and $Q$ are one of 1 and 12, the last remaining number is $L=6$. Therefore, the answer is 6