to find no. of sides

Sum of interior angles of a polygon = 180(n-2) ........where n is the number of sides.

The interior angles are in AP and smallest angle is 120 i.e. first term of AP.

Sum of interior angles =n(2a+(n-1)d)/2

180(n-2) = n(240+(n-1)5)/2

5n²-125n+720 = 0

n²-25n+144 = 0

The polygon can have 9 or 16 sides.

Regards,

Team,

TopperLearning.