Int - Ext = 108, Int + Ext = 180 ---------------------Add the two equations 2*Int = 108 + 180 = 288 ----> Int == 144. Thus the Interior angle is 144 degs. Then the Exterior angle is 180 - 144 = 36 degs. For any convex polygon, the sum of its exterior angles is 360 degs. Therefore, the number of sides of the polygon is = 10. Answer. n = 10: it is regular decagon.