13. Find the number of sides in a polygon if the sum of the measures of the interior angles is 4 times as great as the sum of the measures of the exterior angles. 14. Find the number of sides in a regular polygon if: (a) The measure of an interior angle is 3 times the measure of an exterior angle. (b) The measure of an interior angle equals the measure of an exterior angle. (c) The measure of an interior angle exceeds 6 times the measure of an exterior angle by 12.