Recall that triangles add to 180 degrees. In the left triangle, the angles are 35 + 90 + angle = 180. The third angle of the left triangle is 55 degrees.
Now recall that angles drawn from a straight line all add up to 180 degrees So 55 + 60 + third angle = 180. Thus, the third angle is 65 degrees.
Within the middle triangle, we now have 2/3 of the angles. 90 + 65 + third angle = 180. Thus, the third angle is 25 degrees.
25 degrees is right next to angle X. As we have already stated, they add up to 180 when adjacent.