To get angle 3, we have to angles that are equal, supplemetary or complementary.
In this case, angle 16 is equal to angle 4 and angle 4 is supplementary with angle 3
Angle 16 = Angle 4 = 139 degrees
Angle 4 + Angle 3 = 180 degrees.
Therefore , 180 - angle 4 = angle 3
This gives 180 - 139 = 41 degrees.