Lets draw a picture of the problem:
Since both triangles are congruent, this means that
[tex]\begin{gathered} AB=DE=41 \\ BC=EF=23 \end{gathered}[/tex]
and
[tex]AC=DF[/tex]
which means that
[tex]5x-9=36[/tex]
So, by adding 9 to both side, we have
[tex]5x=45[/tex]
and by dividing both sides by 5, we obtain
[tex]\begin{gathered} x=\frac{45}{5} \\ x=9 \end{gathered}[/tex]
Therefore, the answer is option b
