The following formulae for regular polygons should be known:
Exterior angle = 360º ÷ number of sides
Interior angle = 180º - exterior angle
Sum of interior angles = 180 x (number of sides - 2)
A regular polygon has an interior angle of 165.6º.
How many sides does it have?
Exterior angle = 180 - interior angle = 180 - 165.6 = 14.4º
No. of sides = 360 ÷ exterior angle = 360 ÷ 14.4 = 25