NOTE: You must know the number of sides of each regular polygon name.
The sum of the measures of exterior angles of a regular polygon is 360°
Measure of an exterior angle of a polygon = 360°/n
where n is the number of sides of a polygon
Let x be the measure of an exterior angle of a regular polygon:
a) quadrilateral = 4 sides
x = 360°/4
x = 90°
b) hexagon = 6 sides
x = 360°/6
x = 60°
c) nonagon = 9 sides
x = 360°/9
x = 40 °