Answer:
x = 39
Explanation:
You want to know the measure of the third angle in a triangle in which two of the angles are 39° and 102°.
Angle sum theorem
The angles in a triangle have a total of 180°. That means ...
x° +39° +102° = 180°
x = 39 . . . . . . . . . . . . . divide by °, and subtract 141