Calculate side length as 5 sqrt(3) / 3
the two ends contribute 10 side lengths to the perimeter
each hexagon squished in the middle contribute 4 side lengths
(10 + x ) ( 5 sqrt (3)/3) < 100
shows x < 24.64 sides =====> 6 hexagons in the middle would supply 24 sides
6 in the middle + 2 ends = 8 hexagons would be less than 100cm