Find the number of sides of a regular polygon if one interior angle is 120 degrees.

There are six sides
Because
First, the number of sides and the number of interior angles, both are the same
To find the sum of all internal angles, you use the formula:
(n-2)180=z
where n is the number of sides or internal angles, and z is the angle sum. the letters can be anything
so now, if one interior angle is 120 degrees, then you get the total angle sum by multiplying 120 by n
so just write the equation, and replace z (angle sum) with 120n
(n-2)180=120n
Solve it in any way you like
180n-120n=360
60n=360
n=6
there are six sides and internal angles! This is a hexagon.
FYI, a hexagon's internal angles add up to 120*6=720 degrees