The measure of each interior angle of a regular polygon is 120°. Find the number of sides.

6

Step-by-step explanation:

You can memorize these for the smaller shapes

for equilateral polygons:

triangle: 60

square: 90

pentagon: 108

hexagon: 120

Otherwise, I believe the formula is the total degrees in a polygon (s-2)*180 where s is the number of sides.

So the measure of each angle on average would be (s-2)*180/s.

There (s-2)*180/s = 120

180(s-2) = 120s

180s-360 = 120s

60s = 360

s = 6

(a) the volume of the cone is 20/3 in3

hence, option a is correct.