All angles in a regular polygon are equal. To find the total sum all all the interior angles, we have the formula

(n-2)180.

here, n=the number of sides in that polygon.

since the polygon is a regular polygon, all its interior angles will be equal.

for example,

if the interior angles of a regular polygon is given as 120, you should find the exterior angles at first.

if we are taking a linear pair, we'll get-180-120=60

here, 60 is the measure of each exterior angle. the exterior angles add upto 360. so if we divide 360 by 60, we'll find that there are 6 exterior angles.

which means 6 sides for that regular polygon.(regular hexagon.)

likewise, you can find the answer.