Polygon ABCDEF is a regular hexagon. What is the measure in degrees of angle ABF?
The measure of FAB is just measure of one of the interior angles = 120°
And..in triangle FAB, AB and AF form two equal sides....so the angles opposite these sides are equal.....so....angle AFB = angle ABF
So...
Angle AFB + angle ABF + angle FAB = 180
2 Angle ABF + 120 = 180
2 Angle ABF = 60 divide both sides by 2
Angle ABF = 30°