The gazebo with the longest side length is the heptagon.
A heptagon is a polygon with 7 sides. It has 7 edges and vertices.
The length of the side of a heptagon = (area of the heptagon x 2) / (number of sides x length of the apothem)
= (623.5 x 2) / (7 x 13.6)
= 1247 / 95.2
= 13.1 feet
A octagon is a polygon with 8 sides. It has 8 edges and vertices. The sum of internal angles in 135 degrees.
The length of the side of a octagon = (area of the octagon x 2) / (number of sides x length of the apothem)
= (517.8 x 2) / (12.5 x 8)
= 1035.6 / 100
= 10.356 feet
To learn more about an octagon, please check: https://brainly.com/question/12080203