Help. ​

Isabelle is correct...we use this.....

Ext angle°   =  360 / n     where n is the number of sides

So

72 = 360 / n        rearrange  as

n  =  360 / 72   = 5 sides  [ a pentagon  ]

There is no regular polygon with those conditions that I know of.

C- 5 sides. 

c-5

C-5