For the figure below, if the two triangles are congruent and the side AC = 2x - 4 and side DF = x + 5, what is the value of x?

Remember that
If two figures are congruent, then their corresponding sides are congruent
so
In this problem
The given triangles are congruent
and
AC and DF are corresponding sides
therefore
AC=DF
substitute given values
2x-4=x+5
solve for x
2x-x=5+4