We have 89 and 36 inside of the triangle because 36 is a vertical angle and vertical angles are congruent)
And triangles are equal to 180.
So we add 89 with 36 and get 125 and we subtract 180 with 125 to get the missing angle 55
X and 55 are a linear pair so they are equal to 180.
180-55= 125
I think this is the correct answer X=125
Hope this helps :D