it is known that formula for the sum of the interior angles of a polygon is
sum = (n - 2) 180 (given )
here n is the number of side of a polygon
here we have 6 sides in a regular hexagon
so put n = 6
sum = (6 - 2) x 180
sum = 4 x 180 = 720 degrees.
the sum of all 6 interior angles is 720 degrees,
as all the interior angles are equal in a regular hexagon
so the measure of interior angle (x) is
x = 720/6
x = 120 degrees
so each interior angle is 120 degrees.