The angle adjacent to the 146 degree angle is 180-146 = 34 degrees.
In other words, the angles 34 and 146 combine to 180. These angles are supplementary.
The tickmarks on this triangle tell us it is isosceles. The angles opposite the congruent sides are congruent angles. So the unmarked interior angles (not marked x) are 34 degrees each.
Now use the fact that any triangle has its interior angles always add to 180
