if the exterior angle = 24 the interior angle = 180 - 24 = 156
then we have a rule which is :
the interir angle of a regular polygon =(n-2) × 180° / n , where n is the number of side
so 156 = (n-2) × 180° / n
156n = 180n - 360
360 = (180-156) n
360 = 24 n
15 = n hope it help
so number of sides = 15