$\begin{array} { l }\frac{ 1001 }{ M }=13,& M≠0\end{array}$
Multiply both sides of the equation by $M$$1001=13M$
Swap the sides of the equation$13M=1001$
Divide both sides of the equation by $13$$\begin{array} { l }M=77,& M≠0\end{array}$
Check if the solution is in the defined range$M=77$