9514 1404 393
Answer:
   31
Step-by-step explanation:
The relationship between sides and the sum of angles is ...
   sum of angles = (sides - 2)·180°
Filling in the given value and solving for "sides", we get ...
   5220 = (sides -2)180
   29 = sides -2 . . . . . . . . . divide by 180
   31 = sides . . . . . . . . . . . . add 2
The polygon has 31 sides.