The sum of the interior angles of a triangle is always 180 degrees.
We know two of the angles in this triangle: 36° and 54°.
So, we can find the third angle by subtracting their sum from 180 degrees:
180° - 36° - 54° = 90°
Now we can use the fact that the angles in a straight line add up to 180 degrees.
The angle opposite x is 90°, so the other two angles in the triangle must add up to 90 degrees.
19° + (unknown angle) = 90°
Subtracting 19 from both sides:
(Unknown angle) = 71°
So x is opposite the angle of 71 degrees.