102 Degrees
Angle A and Angle B are supplementary to each other.
Angle A measure = 78 degrees
Find Angle B
We know that in a supplementary relationship between two angles, the sum of both of the angles are equal to 180 degrees.
Here we know that Angle A = 78 degrees
Angle B = 180 - Angle A = 180 - 78 = 102 degrees.