$\begin{aligned}
& \underbrace{A B}{12} \quad \underbrace{\text { MN........Z }}{13} \
& =\underset{\substack{\text { Selection of two } \
\text { leters before } \mathrm{M}}}{{ }^{12} \mathrm{C}_2} \times \underset{\substack{\text { Selection of two } \
\text { leter after } \mathrm{M}}}{{ }^{13} \mathrm{C}_2}=5148
\end{aligned}$