one exterior angle = 180 - 156 = 24 degrees
Recall that the sum of all the exterior angles of a polygon add up to 360 degrees.
So the number of sides in this polygon = number of exterior angles = 360 / 24
= 15
If interior angles was 157 , exterior one = 23 degrees
360 / 23 does not divide to give an integer
so a regular polygon cannot have an interior angle of 157.