You can express the sum of all interior angle of any convex polygon with n sides (n vetices) as 180°*(n-2). From the other side, the sum of all interior angle of any regular polygon is, where is any of its interioir angle. Thus you have this equation 180*(n-2) = n*156. where n is unknown number of sides (of vertices). Simplify and solve for n: 180n - 360 = 156n ====> 180n - 156n = 360 ====> 24n = 360 ====> n = = 15. Answer. 15 sides and/or 15 verices.